HRS Combustion system
This point presents the history, technical aspects and advantages of the High-cycle Regenerative System (HRS) combined with the High Temperature Air Combustion (HiTAC) technology.
Since the beginning of the 90's of the last century almost 800 furnaces has been revamped or built as new units using the regenerative burners, mainly in Japan. About half of them, it means about 400 furnaces, utilized the HRS regenerative burners with HiTAC combustion technology invented and developed by Nippon Furnace Kogyo Kaisha Ltd. (NFK).
First industrial application that used HRS burners took place in 1992. Since that time over two thousand HRS burner pairs have been installed in several industry applications. HRS system has been applied for example in the following areas:
The unique features of the HiTAC combustion technology have been successfully applied in the special HRS Burners. The HRS burner concept depends on the High Temperature Air Combustion with high performance regenerative heat exchangers.
Application of the HRS burners using the HiTAC technology provides the following advantages:
In the HRS burners / HRS combustion systems several techniques are applied in order to achieve the required advantages. The techniques are as follows:
The HRS burner system may operate in two ways: the conventional high velocity combustion mode (F1) and the HiTAC mode (F2). A schematic drawing of the F1 and F2 combustion modes are shown in figure below. During the heat-up the furnace burner works in the F1 mode, however, always as a regenerative burner. When furnace temperature exceeds 800oC, gas is supplied through F2 nozzles and the burner starts to work in the F2 mode.
High-cycle Regenerative System work principle
The idea behind the system is that two burners work alternatively . When burner A works as a burner (the firing mode), burner B sucks the exhaust gas from the combustion chamber (the regenerative mode). The burners change their functions after the switching time. Burner maximum thermal efficiency for such regenerators is achieved during 30-second switching time.
Regenerative heat exchange hardware has a long and outstanding history in reducing industrial processes fuel demand. Excellent thermal properties of ceramic materials, both as a heat storage and heat exchange mediums, give it a clear superiority over common steel heat exchangers. While due to material limitations metallic heat exchangers are limited in thermal capabilities and efficiency, ceramic regenerators allow higher temperatures and heat transfers. Ceramics in many cases demonstrate better resistance against aggressive compounds as well.
Among different types of ceramic regenerative beds the Honeycomb stands out. Ceramic nuggets and balls are both surpassed by the Honeycomb in terms of temperature efficiency, temperature stability, heat exchange surface per volume and mass, lower pressure drop over the bed, lighter weight and thermal inertia.
The HRS burners enclose a regenerative bed called “the honeycomb”, made of ceramics resistant to high temperature of flue gas. The high performance heat exchanger allows combustion air of ambient temperature to preheat up to the temperature close to the sucked flue gas temperature during the regenerative mode of the burner.
Advanced heat recovery
Distributed recuperators and regenerators (like is applied in HRS burner) both share the advantage of being less demanding towards auxiliary burner piping, as lower temperature flue is released from burners and at the same time obtain the best efficiency.
Honeycomb’s bed temperature efficiency can be described by:
nta – air side temperature efficiency
Tao – outlet air temperature
Tai – inlet air temperature
Tgi – inlet flue gas temperature
Actual efficiency attainable varies from over 90% up to 96% with supplied air to furnace contents temperature difference of 50oC.
Excellent fuel efficiency, fuel savings, downsized furnace, increased furnace capacity
The HRS technology was created for fuel savings and successfully meets this goal. High efficiency of the honeycombs results in fuel saving after the revamp of furnaces. The highest level of fuel saving takes place when the furnace before revamping is equipped with a poor recovery system or even does not have one (the savings can reach even about 50%).
The fuel savings for the typical furnaces are on the range of 20% - 35% because of standard preheated air temperature is on the range of 300oC - 450oC and furnace exit exhaust gas temperature is on the range of 900oC - 1100oC.
Ease of deployment and maintenance
Burner setup is easy and adjustment to existing conditions is uncomplicated. The HRS burners do not require complicated maintenance schemes. Burner maintenance is limited to periodic replacement of parts of the Honeycomb bed. Typically after two years of operation top four layers of the Honeycomb bed have to be replaced, however, it depends on process conditions. Replacement after two years of operation are recommended to get reliability of the system, often depending on the combustion and furnace conditions the honeycomb bed can work longer without replacement.
Ease of control
Through simple construction and automatic control system operating the HRS system is easy and integration with an existing system is fast and smooth. Firing power rate can be managed online with both Flow Control and Time Interval Control methods. Burners can be switched on and off during system’s work. All burners on a furnace heating system can operate with a custom switching pattern to regulate power distribution between furnace zones or between burners in a zone. The burners working range covers full 0 – 100% firing power range, individual units as well as the whole system can be operated in stand-by mode at hot conditions without fuel supply.
A continuous increase in ecological consciousness and high pressure to reduce the energy cost in many areas within the companies result in the high interest of industry in applying the newest combustion technology. Thus, every type of new combustion technology has to guarantee reduced energy consumption of the process, low pollutant emissions, a furnace capacity increase, the combustion process and product quality improvement and, at the same time, reliability and dependability in industrial conditions. The presented unique features of the High-cycle Regenerative System (HRS) make this technology the best solution to reach the all goals which are listed above.