Changes in manufacturing processes for the European ceramic industry often occur slowly, over long periods of time, and kilns with the old thick-wall design are still widely in use today. Prior to the development of new insulating methods, ceramic, brick and tile kilns were traditionally built with thick walls to conserve heat.

Unfortunately, thick-wall kiln designs present problems for conventional burners. The nozzles' shorter design causes overheating to occur within the furnace wall, and the burners do not have sufficient exit velocities to allow hot gases to thoroughly penetrate the load. These conditions cause problems with temperature control and heat uniformity, leading to product spoilage from cracking or inadequate curing.

A new burner* has been developed specifically to solve problems inherent to thick-wall kiln applications. Designed to extend completely through the kiln wall, the burner places the flame directly in the kiln for maximum heat and circulation. The burner's nozzle-mix design fires an intense stream of hot gases through a silicon carbide-tipped extended combustor. Using ambient combustion air, this design improves the penetration and circulation of the products of combustion, along with system efficiency.

* ExtensoJet, developed by Eclipse, Inc.

Updated Features

Roof-mounted extended jet burners on the heating zone of a furnace.

The idea of an extended jet burner is not revolutionary. In fact, these burners** have been built for years to meet the needs of old style kilns. The latest burner, however, is based on a standard high-velocity burner and offers a number of advantages. It produces the highest-velocity flame possible, an intense stream of hot gases that thoroughly penetrates the load and delivers precise temperature uniformity for consistent product quality and maximum system efficiency.

The burner's on-ratio control automatically compensates for changes in operating conditions and provides controlled operation over a turndown range of more than 10:1. Direct spark ignition ensures reliable startups, and flame rod supervision monitors the burner for safe, reliable operation.

The burner also offers the convenience of multi-fuel capability with no nozzle change. It can be fired on natural gas, propane and butane. The burner's wide turndown range combined with high excess air means it delivers high-velocity benefits across its operating range. It also offers integrated gas and air orifices to simplify burner piping, setup and adjustment, and air and gas inlets are independently adjustable in 90° increments to suit a variety of piping alternatives.

Available in three sizes with maximum inputs from 250,000 Btu/hr to 750,000 Btu/hr (73 to 220 kW), the burner's gas velocity can be as high as 500 ft/s (150 m/s). The combustor comes in varying lengths from 20 to 56 in. (500 to 1400 mm) and features a silicon tip that is designed to withstand the extreme temperatures of a ceramic kiln. The burners are designed to produce a maximum chamber temperature of 2350°F (1300°C), with a maximum combustion air temperature of 160°F (70°C).

** ThermJet, developed by Eclipse, Inc.

Success Story

The burners are designed to produce a maximum chamber temperature of 2350°F (1300°C), with a maximum combustion air temperature of 160°F (70°C).

In addition to solving the problems inherent with the thick-wall kiln application, many ceramic manufacturers are updating burners to achieve considerable maintenance and fuel savings. One such installation involved the conversion of a tunnel kiln in Europe rated for 285,000 metric tons (314,160 tons) per year of rough ceramic manufacturing. The kiln measured 104.4 m (342 ft) long by 6.7 m (22 ft) wide by 2.7 m (9 ft) high. The process and temperature curves were controlled by a programmable logic controller (PLC). The total installed thermal capacity was 21.4 MW (72.76 MM Btu/hr) on natural gas.

The system was configured with high-velocity burners in the preheat zone (<750°C/1380°F) and with lance burners in the heating zone (>750°C/1380°F) with programmable pulse firing. The first stage of the conversion was to install eight of the new burners in the sidewalls of the preheating zone. The customer was experiencing problems with the roof-mounted lance burners, so these were also replaced with the new burners.

At the second stage of the conversion, one group of 16 new burners equipped with flame detection was installed in the preheating zone, while six groups of 16 burners with no flame detection were placed in the heating zone. No problems were encountered during installation and startup. The new burners were swapped out during actual production, making the changeover even more beneficial to the customer.

The retrofit produced several benefits. First and foremost, the burners significantly improved temperature uniformity. Production flexibility also increased, allowing for the production of more types of products, and reduced heat-up time and better ignition reliability also contributed to increased production. Moreover, fuel consumption decreased dramatically, producing a quick return on investment.

For more information regarding kiln burners and burner design, contact Eclipse at 1665 Elmwood Rd., Rockford, IL 61103; (815) 877-3031; fax (815) 877-3336; e-mail dcollier@eclipsenet.com; or visit www.eclipsenet.com.