Energy-Saving Regenerative Burner Introduced at Keihin Plate MillNKK has installed a large-scale energy-saving regenerative burner in the preheating zone of the No. l continuous reheating furnace of the plate mill at its Keihin Works. The move has proven successful as the mill has lowered its energy consumption considerably. The regenerative burner has been introduced as part of a research project undertaken jointly with the New Energy and Industrial Development Organization (NEDO). The fiscal 1998 project covered field tests for High-Performance Industrial Furnaces. As a result, NKK has confirmed that the new burner has reduced fuel consumption at the Keihin plate mill by about 15%, allowing for the elimination of one of two reheating furnaces at the mill. The regenerative burner was developed jointly by NKK and Nihon Furnace Kogyo (NFK). Known as a high-cycle regenerative-combustion system (HRS) burner, it features a compact device consisting of a ceramic honeycomb regenerator combined with a burner. The regenerator absorbs heat from the high-temperature flue gas generated by combustion in the furnace, then the heat is used to preheat the combustion air and save energy. It is the same type as those already commercially employed for slab reheating furnaces at the Fukuyama Works' hot strip mill and other industrial furnaces. The Keihin system employs a very large device with a maximum combustion capacity of five million kilocalories per hour. The Keihin plate mill has two continuous reheating furnaces, each with a preheating zone, heating zone and soaking zone. Conventionally, in order to save energy, the preheating zone was turned off and the two reheating furnaces were operated for the heating and soaking zones. Installing the new regenerative burner in the preheating zone has allowed energy savings and cut heating time, thereby allowing the use of a single reheating furnace instead of two. The conventional reheating furnaces were equipped with metallic air preheaters (maximum temperature of 550°C). By applying the ceramic honeycomb regenerative burner in the preheating zone, the high-temperature flue gas is now recovered as a source of preheating air (up to 1,200°C), making it possible to reduce fuel consumption per ton/unit by about 15%, from 250,000 kcal to 220,000 kcal. Ecologically speaking, even under combustion using high-temperature preheated air over 1,000°C, the newly developed two-stage combustion technology has made it possible to cut NOx emissions to 30 ppm, which is far below the regulated limit. NKK is planning to conduct a similar joint research with NEDO as part of a fiscal 1999 field test at the batch-type soaking furnace for slabs at the Keihin Works. The company intends to continue seeking the highest level of energy efficiency, while promoting wider applications of high-performance industrial furnaces to contribute to energy conservation on a global scale.
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