Kromschröder burners and controls are meeting the expanding needs of a fused silica crucible manufacturer.
The kiln is equipped with Kromschröder high-performance burners and control components.
A division of Ceradyne, Inc., Ceradyne Thermo Materials, located
in Clarkston, Ga., is a world leader in providing fused silica products for
high-tech industries. A recent facility expansion was undertaken in response to
the solar energy industry’s demand for photovoltaic silicon solar cells, which
represent an important energy source for the future. The facility manufactures
fused silica crucibles used in the photovoltaics process.
Kromschröder UK provided high-velocity BIC
burners and combustion controls used to create the fused silica casting
crucibles. The kiln was designed by Drayton Beaumont, Staffordshire, England,
and the combustion solution includes a complete feature set of components manufactured
by Elster/Kromschröder of Osnabrück, Germany. (Kromschröder products are
represented in North America by Hauck Manufacturing Co., Lebanon, Pa.)
During the manufacturing process, the
silicon is first melted in a crucible. A graphite material surrounds the
crucible and induction heating is used to melt the silicon in the crucible,
transforming it into silicon crystals. The unique properties and the
ultra-high-purity of the fused silica crucibles eliminate the possibility of
silicon contamination inside the crucible. Once the process is complete, the
crucible is destroyed and the silicon ingot is removed.
High-quality fused silica is essential to the manufacture of the crucibles. The
silica is processed and mixed into a slip/slurry. The crucibles are slip-cast
into molds, which are also manufactured by Ceradyne, and the green crucibles
are then dried, fired and cooled in periodic kilns.
The kilns are equipped with Kromschröder high-performance burners
and control components. High-cycle-duty valves and regulators, along with
burners with high turndown capability, are essential to providing a
fuel-efficient pulse-fired combustion system, particularly one that is required
to perform multiple functions. Accurate temperature control (± 1ºC) and
superior temperature uniformity allow the kilns to be used for cycles that include
drying, firing and cooling.
Each kiln is equipped with 24 high-velocity
Kromschröder BIC burners arranged in 12 two-burner zones. The burners are
pulse-fired in pairs. Pulse-fire control utilizes the high-velocity burner at
its maximum velocity by operating the individual burners on/off. The timing
between each burner cycle is determined by the temperature demand and pulse
algorithm in the PLC. The burners are fired in a random pattern to increase the
circulation within the kiln. Pulse firing provides the highest fuel efficiency
and greatest degree of temperature uniformity, and is the ideal type of control
system for many industrial heating applications.
Features incorporated in the Kromschröder components provide operational
advantages not available from other combustion equipment and ensure an
economical solution for the crucible firing process. Each burner features a
continuous internal pilot with a spark-and-sense electrode, which serves the
dual purpose of spark ignition and flame sensing of the pilot flame. The pilot
air and gas are regulated to provide accurate flows and allow high burner
turndown. An ionization rod is included with the burner and is used to detect
the main flame.
A Kromschröder air butterfly valve with a direct-coupled electronic IC40
actuator at each burner is cycled on and off during the firing cycle. The
butterfly valve design, in conjunction with the actuator, provides a very low
leakage rate and almost zero hysteresis.
Operating settings were programmed into the actuator via BCSOFT, a package
developed by Kromschröder that allows a PC interface to be used to initialize
and exchange settings data between components. Via BCSOFT, the settings were
duplicated and loaded into the other actuators, which shortened commissioning
time and eliminated the possibility of error or tampering with linkage and
desired control settings.
The Drayton Beaumont kiln control system is PLC-based. The touch screens allow
kiln operators to closely monitor the combustion system. Start-up screens, kiln
overview screens with burner and pulse status, temperature loop tuning screens,
first-out annunciation, and other operator screens provide a user-friendly
Each burner features a continuous internal pilot with a spark-and-sense electrode.
Kromschröder’s VAG combination shutoff valve and ratio regulator
control the gas flow to each burner. The
ratio regulator is cross-connected downstream of the air butterfly valve. As
the air increases with the opening of the butterfly valve to the high position,
the gas increases in proportion. A built-in limiting orifice in the burner is
used to set high-fire gas flow for optimum fuel air ratio. Low-fire gas flow is
adjustable on the front of the regulator housing. The VAG’s long-life,
high-cycle-duty solenoid is controlled by the PLC once the pilot flame is
Burner control is provided via a Kromschröder BCU 480 burner control unit
supplied for each burner. The unit has a built-in ignition transformer and two
flame amplifiers. The BCU controls the ignition process and continuously
monitors the pilot and main burner flames. A digital input signal from the PLC
is provided to the BCU, which controls the IC40 for the on/off pulse firing of
the main burner flame.
The closing of the gas valve is delayed
until the air valve has reached its low position, assuring complete combustion.
The BCUs are mounted at each burner to reduce installation costs and simplify
installation, commissioning and troubleshooting efforts. A second
pneumatic-actuated main air valve is located at each burner to provide
additional air during the cooling cycle.
A modular safeguard control unit.
Gas Delivery and Safety
The main gas fuel train is a complete Kromschröder
system consisting of components for gas filtration and regulation with
overpressure protection, as well as modular safeguard controls and fuel
metering. A JSAV overpressure shutoff valve, also known as a slam shut valve,
is piped upstream of the VGBF pressure-reducing regulator for protection
against high gas pressure to the downstream components.
The main gas train includes Kromschröder’s
latest modular safeguard control unit, the Valvario. The VCS, an FM- and
CSA-approved double shutoff valve, is equipped with tightness control in lieu
of a proof-of-closure switch. Also known as valve-proving controls, the TC
module, upon startup of the gas train, verifies if the two solenoid safety
shutoff valves have an acceptable leakage rate as determined by the appropriate
If an unacceptable leakage rate is detected
by the valve-proving controls, the TC activates an alarm and locks out the
combustion system until the problem is resolved. Low and high gas pressure
switches are flange-mounted to the side of the valve body to complete the
safeguard control package. A relief valve is located directly downstream to
vent trapped gas between leak tests.
The main gas fuel train system consists of components
for gas filtration and regulation with overpressure protection, as well as
modular safeguard controls and fuel metering.
Worldwide customers choose Ceradyne Thermo Materials’ crucibles
over those of other manufacturers for their high reliability, fully traceable
production and purity data availability, and outstanding customer service. The
quality workmanship of the new kiln and combustion system, along with expedient
installation and trouble-free commissioning, allowed Ceradyne Thermo Materials
to bring the kiln online one week after complete installation and start-up
The increasing demand for crucibles has required Ceradyne Thermo Materials to
procure more kilns. The performance of the first kiln resulted in a contract
for two more Drayton Beaumont kilns equipped with Kromschröder burners and
controls to meet ever-rising production demand.
For more information, contact Hauck Mfg. Co. at Box 90, Lebanon, PA
17042; (717) 272- 3051; e-mail email@example.com; or visit www.hauckburner.com. Ceradyne Thermo Materials can be reached via
e-mail at firstname.lastname@example.org or online at www.ceradyne-thermo.com.