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The periodic kiln found in most of today’s ceramic plants has a ceramic fiber internal lining, a multi-deck setting, a downdraft exhaust configuration and two- or three-zone temperature control. While this configuration offers good overall firing results, it does have certain drawbacks. The interaction between adjacent kiln car settings from variations in load weight can lead to relatively high temperature differentials throughout the kiln, as well as preferential product placement requirements. Additionally, the exhaust flue construction in these kilns is usually complicated. And these systems are often expensive and take up a large amount of space within the plant.
Recently, a new periodic kiln was introduced that overcomes all of these challenges. With a modern updraft exhaust design, the new kiln occupies a small footprint and produces vastly superior temperature uniformity through the use of multi-zone, computerized temperature control. Each kiln car has two separate control zones and maintains ideal pressure conditions.
The New Kiln in ActionThe first of this new generation of periodic kilns were built for Trent Bathrooms Ltd. in England, now part of Southern Ireland-based Qualceram Shires PLC. The two natural gas fired kilns have a 65 m3 setting capacity and produce approximately 450 fired pieces on an 11.0 hour firing schedule. The kilns are complemented by a fully automated kiln car handling system.
Trent Bathrooms, whose client base includes such prestigious names as Windsor Castle, set a demanding list of criteria for the new kilns, including improved firing efficiency, lower operating costs, greater flexibility and optimum product quality and yield. The kilns met all of these criteria—and offered some additional benefits besides. They feature a modular low-thermal mass design for rapid on-site installation; a high density ceramic fiber lining system; stainless steel combustion piping; and low pressure operation, providing long life for both kiln and kiln car linings. Additionally, sophisticated, fully automatic firing controls in 12 zones provide exact temperature distribution, zero firing losses and fully random product placing. Bullers rings spread throughout the kiln provide an accurate measure of heat work distribution, while sophisticated cooling systems enable rapid cycles to be completed, and a patented Dri-lok™* kiln car superstructure provides maintenance-free kiln car edges.
According to Trent Bathroom’s group ceramic production director, Alec Gemmell, “Both kilns went straight into production, with no commissioning problems, and the back-up service provided has been first class. The bullers ring spread and temperature uniformity from the kilns are remarkable. I can only speak highly of the kilns’ overall performance.”
A PLC-Controlled SystemKey factors behind the kilns’ performance are the high velocity burners, arranged in a multi-zone configuration, and a pressure damper system that maintains optimum kiln pressure levels at all stages of the firing cycle. At the heart of the kiln control system is a rugged, industrial PLC comprising off-the-shelf modular hardware and software components. The PLC controls all the major kiln functions, with the exception of the hardwired safety circuits, including direct temperature control and profile generation.
A large, color touch-screen operator display has radically improved the presentation of kiln data with a simple, menu-driven navigation scheme through all areas of the control system interface. The operator can simply touch the button marked “Control Loops” to see the kiln control loops displayed—including setpoint, measured variable and output power—or move to “Alarms” to see a full list of active or historic alarms, time- and date-stamped. All configuration and program data are fully protected behind an “engineers” password facility.
To start the kiln’s firing cycle, the operator selects the required program and presses the “start” button. The kiln progresses through a fully automatic start sequence, and a scrolling banner indicates progress through the start-up safety checks.
This type of control and display system provides Trent’s operatives, engineers and maintenance staff with a level of user-friendliness rarely seen in the ceramic industry. Compared to traditional instrumentation, where this process has to be performed with a number of multifunction pushbuttons, the popularity of these interfaces is easily understood.
A Periodic Shuttle KilnBased on the overwhelming success of these two kilns, Trent’s sister company, Shaws of Darwen Ltd., requested a similar kiln to fire large, fine fireclay products, with some individual pieces weighing up to 60 kgs (132 lbs). The intended site for this particular kiln was subject to a width restriction, preventing the use of a conventional transfer car system for kiln car movement. Instead, the kiln was designed on a “shuttle” principle. Access to doors at both ends of the kiln is provided with a straight-through car track.
Firing such large pieces places an even greater demand on the need for close temperature control at all stages of the firing and cooling cycles. Correct burner configuration is essential in achieving this close control. Burners are arranged to operate in pairs, firing underneath and above the kiln car setting, with each pair of burners forming an individual temperature control zone.
As with the Trent kilns, an Omron PLC system controls all kiln functions and is linked to a touch-screen computer, which runs Intellution FIX32 control and data acquisition software.
Not Just for SanitarywareThis new generation of periodic kilns has been a springboard for many new orders in the sanitaryware sector, both in the UK and worldwide. And the technology isn’t just limited to the manufacture of sanitaryware—the multi-zone firing design is equally applicable to other industry sectors, including tableware, heavy clay products and high temperature refractories. Through this new technology, manufacturers can experience easier operation, consistent high yields and product quality, low operating costs, durability and low maintenance requirements in their firing operations.
For More InformationFor more information about fast firing sanitaryware in a periodic kiln, contact Pearson at Drayton Kilns Ltd. UK, Newstead Trading Estate, Trentham, Stoke-on-Trent, Staffordshire, England, ST4 8HX; (44) 1782-657361; fax (44) 1782-658946; e-mail firstname.lastname@example.org; or visit http://www.draytonkilns.co.uk.
*A trademark of Premier/Hepworth Refractories