In an effort to increase output rates, Richard Ginori turned to a control system from Ascon SpA for its Sacmi Forni tunnel kiln.
Often called white gold
high-quality porcelain tableware is a precious, sonorous material characterized
by a bright white color with light blue shadows, almost transparent thickness,
and good mechanical strength. These characteristics can only be obtained by an
appropriate firing in the kiln; other production stages cannot satisfy the product's
Control, automation and supervision are essential in any
ceramic production plant where efficient management and high output rates are
required. If the production includes high-quality porcelain, the combustion
control of the kiln becomes one of the most important aspects of the production
cycle. Porcelain tableware production uses dedicated shuttle or continuous
tunnel kilns loaded with cars and outfitted with combustion control systems
that allow a controlled firing in a reducing or neutral atmosphere in each
Richard Ginori, established in Florence, Italy,
in 1735 and a leader in the production of high-quality tableware, was recently
looking to improve the production of its Classic line of art design tableware.
The company's main goal was to drastically increase its output rates, so it
turned to Ascon SpA for an instrumentation and control system for its Sacmi
Forni tunnel kiln.
The Need for Control
Richard Ginori's final product requirements include white
color, transparency and high mechanical strength, and the production cycle
includes the preparation of raw materials, casting, drying, glazing and firing.
The porcelain's white color is obtained by eliminating the iron oxide present
in the slip, while mechanical strength is achieved through appropriate
Iron oxide, which produces undesirable yellow shades in
the finished product, is eliminated by controlling the firing to obtain a
reducing atmosphere. To obtain the necessary mechanical strength of the thin
porcelain, it is necessary to accurately control the firing temperature and
ensure the correct sintering of the slip. The kiln temperature control acting
on the combustion, combined with the reducing atmosphere control acting on the
air/fuel ratio (corrected based on the carbon monoxide measurement), solve both
problems with control strategies downloaded into Ascon's AC Station series
programmable loop controllers. Ascon developed the control system in close
cooperation with Sacmi Forni, part of the Sacmi Group.
Figure 1. Schematic of the reducing atmosphere combustion
control of one zone of the tunnel kiln.
The kiln has eight firing zones with eight gas burners
each. The high number of burners and adjustment zones, the control system, and
the efficient insulation guarantee progressive, uniform and flexible heating,
as well as low fuel consumption. The gas flow and combustion air flow of each
zone are measured through orifice flanges connected to transmitters, which
include temperature change compensation for the air flow (see Figure 1).
The carbon monoxide (CO) content of each firing zone is
measured by an infrared analyzer that scans the eight sampling lines of the
zones under control. The signals representing the gas and air flows and the CO%
are fed, along with the zone temperature, into the AC Station multi-loop
controllers. The control strategy software manages:
- zone temperature
- fuel/combustion air stoichiometric ratio
- adjustment of the fuel/air ratio on the basis
of the requested % of CO
- setting of the air and gas flow control valves
Burner heads on one side of the kiln, along with the
related piping and the flow transmitters of the gas and combustion air.
One controller is used for each zone and includes, in
addition to the kiln temperature and CO inputs, two PID control loops-one for
combustion air and one for gas. This setup also allows the operator to view an
interface graphic display for each zone on the 72 x 144 mm front of the
Each zone has its own temperature and its own atmosphere.
The first zones fire in a reducing atmosphere to eliminate the iron oxide,
while the last firing zone has a neutral atmosphere. Pressure control prevents
external air from entering the kiln, thus creating an oxidizing atmosphere.
Pressure control, which is essential since the kiln inlet and outlet are open,
is managed by separate AC Station controllers that adjust the speed of the flue
gas exhaust fans. The cooling stage is indirect to avoid oxidizing the load.
The combustion control system is interfaced with the
automatic ignition system and the flame control. The kiln is approximately 48 m
long with a useful car width of 1500 mm, and can complete a load cycle in 6
hours. The temperatures in the firing zones range from 1200 to 1350°C. In the
zones with reducing atmospheres, the reducing level is kept low (4 or 5% of CO
are the most common adopted values).
The kiln inlet (right) and the dryer outlet (left).
Control with Ease
The plant also includes the control of the slip
production machines and the dryers. The design of the control strategies was
simple through the AC Station's AC Prograph graphical programming software,
which uses the function block method. A function block diagram (FBD) can
replace thousands of lines from a textual program. Graphical programming is an
intuitive method of specifying system functionality by assembling and
connecting function blocks.
An FBD network primarily comprises interconnected
functions and function blocks to express system behavior. Function blocks were
introduced to address the need to reuse common tasks, such as proportional
integral derivative (PID) control, counters and timers, at different parts of
an application or in different projects. The wide range of function blocks
available in the software results in the simple integration of the analog
functions with the logic and sequencing functions.
The operator interface is a high-definition graphic
display with several pre-formatted pages that feature numerical values, bar
graphs, trends, alarms and menus. The control and monitoring systems are
interfaced with a supervisory control and data acquisition (SCADA) system that
provides plant supervision and management information, including the
determination of the set points, recipes, alarms and data acquisition.
Immediate results indicate that the system has been
successful in maximizing the production at this facility. Product quality has been dramatically
improved while throughput has increased with an added benefit of improved
"This new Ascon control system has shown benefits
from the very beginning," said a company representative from Richard
Ginori. "It is difficult to put exact numbers on system performance, but
we can say that the payback has been less than one year. We couldn't be more pleased with Ascon and
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