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Harchris has recently completed the rebuild and commissioning of its Number 10 Pit Furnace, improvements that mean that the company now sports the first furnace with recuperative burners and ultra low NOx emissions in South Africa
The project was completed in record time as a result of the collective effort between Hotwork Combustion Technology in the UK that engineered the modification of the furnace, Harchris’ maintenance department as well as local engineering company Talec that supplied the control panel and commissioned the furnace on behalf of Harchris.
According to Harchris’ managing director, Errol Preston, the company is exceptionally proud of its achievement, “The deployment of this furnace will not only improve our energy consumption, and assist in protecting our fragile natural resources, but it will also drastically and dramatically reduce our existing carbon footprint while providing our business with significant cost savings and benefits.”
The new furnace is equipped with two Hotwork EJ06-12 Hot Air Burners positioned to fire tangentially at opposing corners of the pit furnace, and each burner has been coupled via an insulated duct to a single Hotwork Compact Recuperator that provides preheated air to the burners. The Recuperator is positioned to encourage hot gases to re-circulate around the furnace improving heat transfer to the load.
An auxiliary flue has been located on the opposite wall of the furnace to provide an additional spill-off for optimum pressure control. Each burner is fitted with a flue gas recirculation duct that is positioned at a low level; this also improves waste gas recirculation within the furnace. The system has been designed to operate in Pulse fire, Modulating, or Excess air mode so that greater flexibility, due to the varying operating temperatures and cycles required of the furnace, can be achieved. The system was designed to comply with European Standard EN746-2.
Harchris is now able to take advantage of benefits such as excess air control in low temperature cycles, modulation of the gas flow and modulating control for high temperature cycles and pulse-firing control for high temperature cycles. The additional benefit of pulse firing is that the burners are either operating at their maximum or minimum rate, therefore maximising efficiency of the combustion system.
“One of the primary functions of any combustion control system is to vary the heat input required by individual processes. In pulse firing mode, the heat input is controlled by modulating the frequency of operating the combustion burner or burners,” states Preston. “With the new burners we can fire them at high fire for controlled times and then cycle them back to a lower fire or simply turn them off, all of which we are able to control through the new process controller.”
“It is with this concept that pulse firing is often referred to as frequency-modulated firing as each burner is controlled independently of other burners, resulting in a great deal of control flexibility and precision. In short, pulse modulated firing allows for more precise control and in turn better performance”.
The true benefits of a pulse firing system such as that, which has been deployed in the Harchris Furnace 10, includes more precise and flexible control of the basic combustion process as well as more consistent and precise control of the air to gas ratio and of the energy input to the system. Where proportional systems fail to deliver, pulse firing allows for unprecedented burner control.
“In Furnace 10 we are now able to control the frequency and timing of firing of each burner at carefully metered fuel inputs,” said Preston. “As each burner now comes with its own air valve and gas regulator, there is little wastage or unnecessary firing of the burner while it is not in use.”
Another benefit comes by way of better temperature uniformity as a result of the fact that each burner is individually controlled. Burners can also be zoned more flexibly and it is easier, and more cost effective to have numerous zones of control. Gas circulation is now maximised and temperatures are better set and more uniform.
“We are also seeing greater process control flexibility with the ability to make use of an entirely computer managed system, negating the need for cumbersome and error prone, manual systems,” he says. “Our system is able to function in heating-only as well as in a heating and cooling mode which enables the rapid reduction of temperatures as well as the almost instant refiring of the furnace dependant on the demands of the heat treatment process at hand.”
According to Preston other benefits include improved productivity of the furnace as well as higher product quality and fewer losses as a result of temperature uniformity and temperature control. Fuel savings are now also dramatically improved as Harchris is now able to maintain precise gas to air ratios throughout the firing process, ensuring close to "perfect" combustion (a 10:1 ratio with natural gas) at the peak firing temperature in both continuous and periodic furnaces. The company has calculated that its savings will be between 20-25% in the future.
“One of the contributing factors as to why we opted for the Hotwork EJ06-12 Hot Air Burners is their ability to reduce air pollution, something of critical importance on all industry’s carbon footprint checklist,” mentions Preston. “We are able to achieve this with the more precise control offered by pulse systems and the state-of-the-art E-Jet Ultra Low NOx Burner technology used. We can keep the NOx, or mono-nitrogen oxides NO and NO2 levels much lower and attain actual levels dependant on peak firing temperature.”
As a result of the computerised electronic controller as well as the individual flame monitors that have been built into each burner, Harchris is also able to take advantage of enhanced safety features for each burner as the loss of one flame monitor signal for whatever reason does not interfere with the operation of the other burners in the system.
“The furnace is truly revolutionising the way we work as we are able to achieve ultra low NOx levels through the combination of a range of NOx reducing techniques which include an innovative feature, developed by Hotwork, the Internally Induced Fuel Dilution System," said Preston. "Additionally the Hotwork E-Jet Burner can also operate with internal Flue Gas Recirculation (FGR) without the need for hot gas fans and associated refractory lined ducting. The addition of a local FGR duct and the flexibility of installing it in a strategic location around the burner also improve temperature uniformity, a major benefit for applications such as heat-treatment. Which is after all the cornerstone of the Harchris business."