• The Glass melting recuperative furnace is the most used furnace for medium production of tableware, head car lamps, glass isolators and transparent and green containers glass.
• Its standard dimensions are between 10 and 80 tons / day.
• It has a steel hot air recuperator with a max. pre-heating temperature of 800°C
• The average life time is 10 years for the refractory materials of the melting tank.

ADVANTAGES OF THE U-MELTER SYSTEM IN FURNACES OF SMALL-MEDIUM DIMENSIONS

Until the sixties, all furnaces had END PORT burners because the only fuel used for melting was heavy fuel. This fuel, in comparison with the methane gas, burns more slowly and thus produces a much longer flame.
This is the reason why in the past the burners were placed in the end side of the furnace and never across it.
With the arrival of natural gas in the factories, designers initially tried to change only the burners, leaving unchanged the design of the furnaces.
In about 15 years however, designers have almost completely abandoned the solution of the END PORT burners, in favour of the so-called cross fire U-melter system.
The only exceptions to this practice are represented by very small furnaces (for reasons of easiness and cost) and those exceeding 40-50 tons, which use huge and expensive regenerators and recuperators of refractory metal to heat the combustion air. The reasons why the cross-burning furnaces have better performance and better consumptions are the following:

• Larger surface area of heat exchange between the flame and molten glass
• Creation of currents in the glass, which promote fusion and refining. The sketch here below, explains the first reason.

We can see how the flames of two burners (on the left, Figure 1) cover less area than four burners (on the right, Figure 2).

Besides, in the first case the flames exchange the heating with the raw material (Figure 1) that enters in the furnace, while in the U-melter system the heat exchange occurs between the flame and the molten glass (Figure 2).
The exchange of heat between the cold composition and the hot flame is much less than the one which occurs between the hot glass and the flame. In fact, the molten glass is a good conductor of heat, while the composition behaves as an insulator and acts as a screen between the flame and the liquid glass.

We can say that, having the same surface of the melting tank and the same quantity of raw material charged, the U-melter furnace (Figure 2) on the right can work at a temperature of 20-30 degrees lower.

The side burners create a hottest zone in the furnace, called refining area.

In this area the glass heats up and tends to rise to the surface, where it reaches its maximum temperature. The heating and the upward movement, cause the refining of the melted glass, that is to say to lose the gas bubbles created by the dissociations of the components of the mixture. Another positive effect on the furnace functioning is given by the current of hot glass that heats the mixture that has just entered the tank, and thus promotes its melting.

Data Sheet

• Number of sidewall burners From 4 to 20 burners
• Melting capacity Range: From 10 to 80 tons / 24 hours
• Melting area range From 10 to 40 m²
• Glass type and color: High quality soda-lime flint and colored glass
• Melting temperature: 1550°C
• Length/width ratio: 2,1/1
• Specific melting rate: From 1 to 2 ton/ m²
• Number and type of batch chargers: One oscillating type charger
• Type of energy: Natural gas or heavy oil
• Preheating of combustion air: Double shell steel recuperator till 600°C - Tubes bundle recuperator till 750°C
• Energy consumption: 50 ton per day furnace with tubes bundles recuperator 750°C hot air, energy consumption 1700 kcal/kg of glass

Heat Recuperator 'Tube bundle' Data Sheet

• The standard design consists in a cylindrical tube bundle, made with tubes 253MA steel, which is installed in a vertical shaft insulated with refractory material. This shaft is located directly on the furnace chimney.
• This recuperator produces a max. air preheat of 800°C and it can receive waste gas at 1600°C.
• The tube bundle heat exchanger is composed by tubes mounted on a double shell with cylindrical shape, made of an inside cylinder in refractory 253 MA thickness 5 mm.
• The tube bundle recuperator can be combined with a second recuperator double shell type, in order to improve the heat exhange.

ENERGY SAVING

The energy saving of such recuperator is very high, we normally calculate that every 100°C of temperature of the combustion air, corresponds to 5% of energy saving. It means that with a heat recovery system 'tube Bundle' recuperator the energy saving is between 40 -45%.

STACK BASE VALVE

At the stack base of the chimney a security valve will be installed. This valve is necessary to avoid the overheating of the recuperator in case of lack of electric energy or stop of the air fan (this event is very dangerous for the refractory steel inside of the recuperator). In this event, the valve opens automatically and cold air goes inside, keeping the steel temperature below the dangerous level.

A thermocouple K type is mounted in the outlet air pipe and it is connected with a digital regulator where the operator sets the working temperature. In case of overheating of the combustion air, the digital controller drives the opening of the security valve (see the sketch below).

Heat Recuperator 'Double shell' Up to 600°C Data Sheet

• This type of recuperator consists in two cylinders of similar diameter made with heat resistant steel and insulated outside with ceramic fiber and rock-wool. The heat exchanging area is the anular space formed between the two concentric cylinders: in fact the hot waste gas passes through the inner tube, heating the steel till 800°C, and the combustion air passes through the anular space cooling the steel and heating up itself till 600°C.
• The stainless steel inside of the recuperator is available in two qualities: AISI 310S and 253MA.
• The double shell recuperator can be used in single modules or in double modules with two recuperators one after the other.
• This kind of recuperator is used for furnaces of small dimensions up to 50 ton / day.
• The double shell recuperator has a overheating safety system installed on the refractory material of the chimney. This system consists in a stack base motorized valve, that through a cold air flow, regulates the temperature of the waste gas in the chimney in case of overheating, and cooling the recuperator in case of stop of combustion air flow (due to black out or electroventilator breakage ).

Hot air control stack base

• The Double shell recuperator has a overheating safety system installed on the refractory material part of the chimney. This system consists in a stack base motorized valve, that through a cold air flow, regulates the temperature of the waste gas in the chimney in case of overheating and cooling, the recuperator in case of stop of combustion air flow (due to black out or electroventilator breakage).
• This system allows to have a longer life of the recuperator and avoids any possible overheating of the refractory steel.
• The system consists in one motorized butterfly valve installed on the basis of the chimney. This valve is connected to a thermocouple on the hot air piping, through a digital controller (see the sketch).
• The controller receives the temperature signal from the thermocouple and manages the set temperature of the hot air, opening and closing the cold air flow.
• The servomotor is armed with a strong spring that in case of lack of electric energy opens completely the butterfly valve.

Furnace Construction

• The demolition and reconstruction of the furnace are the most demanding operations in the realization of the plant.
• FALORNI company has a very specialized and experienced technical staff, able to deliver the furnace completely assembled and started into production, including the pre-heating of the whole plant.

 

Combustion Systems

The combustion UNITS are pre-assembled into a steel frame unit, delivered fully piped, wired and tested.

Each gas line in the Natural gas combustion ramp is composed by:

• Gas Filtration
• Flexible joint
• Gas Pressure regulation
• Shut off valves
• Safety valves
• Gas Flow measure transmitter
• Air Flow measure transmitter
• Motorized gas valve for control
• Manual by pass electric valve set
• Air Fans controlled by inverter

AIR REGULATION

The air Digital controller drives the electronic inverter and it makes vary the fan motor's turns. An electronic device, through a calibrate orifice, measures the quantity of air and sends the input to the electronic gas flow controller.

GAS REGULATION

The gas flow controller makes the matematic ratio based on the air quantity, and controls the gas flow through a motorized valve. On the gas pipe there is a calibrated gas orifice with an electronic differential pressure transducer device.

 

TEMPERATURE CONTROL

The target temperature is set on the main controller that controls air and gas controllers. Programs for different thermal cycles can be performed.

AIR CONTROL

The air controller controls the electronic Inverter that changes the speed of the fan. Fan motor always runs at minimum speed. Then energy consumption and noise are minimum.

GAS CONTROL

The gas flow is controlled through the electric valve operated by the gas controller.

AIR/GAS RATIO

The system checks any time the proper quantities of gas and air to the burner.

• 1. Temperature controller
• 2. Gas controller
• 3. Air controller
• 4. Air flow transmitter
• 5. Heat recuperator
• 6. inverter
• 7. Air valve
• 8. Fan
• 9. Thermocouple
• 10. Gas valve
• 11. Main gas valve
• 12. Flexible joint
• 13. Filter
• 14. Gas reducer
• 15. Shut off valve
• 16. Gas flow transmitter
• 17. Gas controller

Control Systems

AUTOMATIC COMBUSTION CONTROL

All the main furnace process variables are automatically controlled by precision closed loop controllers. The signals, derived from a comprehensive set of plant sensors, are taken to a central control and instrumentation panel. Manual by-pass switches are available for all variables for setting up or emergency use. From the central control panel it is possible to start and check all the plant, both the melting tank and the gathering bays or channels areas and spouts.

Control and instrumentation panel including:

• Operation selector and push buttons for the complete furnace (melting area, pressure, glass level, gathering bays or forehearths).
• Furnace temperature controllers (melting and refining) Eurotherm.
• Gas flow digital controller Eurotherm.
• Air Flow digital controller Eurotherm
• Hot air digital controller Eurotherm
• PLC Signal processors for alarm status acquisition (alarm call – alarm knowledge - alarm restore)
• Furnace Pressure controller
• Glass level controller

Furnace and Forehearths Automatic Control

The system is designed to collect and store the most important furnace system parameters so that the operators can have online access to all information. The software main features available:

• System communication with the furnace control PLC located in the control room, allowing the management of all relevant functions from keyboard.
• Historical trending: the program can trend all events and display them in a graphic form. It replaces the traditional recorders and enables correlation between the variables.
• The memory capacity is sufficient to store the whole furnace campaign.
• Historical alarm: the program will record all alarms, the time when the alarm goes off, the moment when the operator detects the alarm, the time of return to the normal variable.
• Moreover, the program can trend all events, set-point changes, alteration of the alarm sets, manual variations at the regulators exits etc.
• Daily reporting will be designed according to the Customer's requirement

 

Hot Air Burners

• Hot air burners for unit melter furnace. The internal part is covered with refractory material; the maximum temperature of the air is 750°C.
• On each burner, a butterfly valve with pressure manometer for Hot Air regulation.
• On each Burner, a Micrometric valve and mechanical gas flow meter for gas quantity measure.
• The gas mixer of the burners are adjustable in order to control the flame length. The distance between air mixer and gas nozzle inside of the burner is adjustable, in order to control the air gas mixing process.
• The gas pipe with nozzle and air mixer are easily interchangeable from the back of the burner.
• The burners can work with big excess of air to create a very oxidant atmosphere in the combustion chamber.
• Low noise burner. The combustion noise of these burners is very low.
• The burners are installed on a fully adjustable bracket and connected to the gas supplied through quick-release flexible hoses.

 

Glass Level Control

The glass level system with tip platinum probe, guarantees a 0,1 mm precision for the variation of the glass level.

The Probe can be:

• High temperature steel water cooled probe, with tip in platinum of about 20 mm.
• Alumina probe, high temperature resistant with tip in platinum 20 mm.

The Control of the Glass Level: The probe has a continuous alternate movement (up and down). When the platinum tip of the probe touches the glass surface, the electric circuit closes; the moment of the contact is underlined through a potentiometer, that records the exact position in which this contact happened. The probe stops suddenly and inverts the movement in order to avoid to plunge the platinum tip into the glass.

The signal coming from the potentiometer is converted from KΩ to mV, and sent to a PLC.

The signal is subsequently sent to a regulator/programmer Honeywell UDC 1002, which shows on its display, the position of the glass in mm as regards the theoretical zero.

The output of the instrument which makes the level regulation is in 4-20 mA and is connected to the regulation panel that drives the raw materials' charging machine

Laser Ray Glass Level Control

The device is composed by 4 units:

• Laser source unit;
• Receiver unit;
• Indication unit (display) and regulation (to be supplied under request);
• Terminal box unit;

METHOD OF MEASURING AND STRUCTURE (CONSTRUCTION)

• In its melting state, the glass has a uniform and flat surface (smooth) and has reflecting capacities. This capacity of the glass is exploited in the method of glass level measuring without contact, with the help of the laser.
• The laser ray, from the laser source unit, falls on the melting glass surface, with an angle of 8-45 degrees, and it is reflected on the graduated line of the photo-receivers of the receiver unit. According to the glass level, the laser ray moves along on the graduated line of the photo-receivers. The modification of the glass level in the field of ± 10 mm, causes the movement of the laser ray of ± 20 mm on the photoreceiver. The integrated processor processes the signal received and calculates the glass level.
• The scheme of the digital process of the glass level measurer LUR-4C signal, allows to minimize the effect of external perturbation elements: vibration of forming machines, flame tongues, electric perturbations.

Pressure Control

Complete furnace pressure metering and control system, including:

• Furnace pressure probe
• Sensor for atmospheric pressure measuring transmitter.
• Digital controller Instrument
• Electronic inverter
• Electric fan
• Air Jet damper

PRESSURE REGULATION SYSTEM

The control of the pressure is regulated by the inserting of plus or minus forced air, in the waste gas exit pipe, after the recuperator. In this way we can reduce or increase the speed of the waste gas and consequently the pressure inside of the furnace.

THE SYSTEM IS COMPOSED AS FOLLOWS:

The differential pressure value coming from the furnace pressure probe is received by the pressure transmitter that transforms it in electric signal and sends it to the digital controller. The automatic digital controller manages the air quantity (electric fan speed) through an electronic inverter.

Batch charging machine

The furnace is provided with "DOG HOUSE" with trapezoidal shape. The batch is charged by Falorni oscillating / rotating water cooled charging machine. The machinery have two movements: the oscillating pusher that pushes the batch head in the glass, and the rotating 90° movement that distributes the batch on a larger glass surface.
In details, the charging machine achieves: the complete covering of dog house; a very good distribution of mixture on glass surface; the absence of false air infiltrations and so reduction of Nox; the absence of dust in the dog house.
The Falorni batch charging machine is covered in the internal part of the hopper and in the pusher, with very hard coating of 5 mm thickness of wear protection.

Forehearths Technology

The Falorni Forehearth has been studied for reaching the two main important technical features:

• The best temperature homogeneity of the mass of glass.
• The lower energy comsumption of the complete forehearth.

At the end of the channel, in the equalizing zone, there are three thermocouples with 3 points each one: the 'Temperature gate' is where the homogeneity of the temperature of the mass of glass is measured.
The main important features of the Forehearth are the followings:

• Accurate combustion control with single or double (separate) control in each zone of the channel.
• Accurate cooling control of the superstructure (central area of the glass surface) and also the bottom of the channel (through special blocks with cold air passage holes).
• Complete supervision control and very friendly use monitoring system with double PLC.

Forehearths automatic control

Accurate automatic combustion and cooling control. Every heated / cooled zone has the possibility to regulate the temperature in order to reach the best homogeneity of the mass of glass. The system has three chimneys for every heated cooled zone. Each chimney is regulated by an automatic air jet valve. With this system it is possible to move the hot spot of temperature in the glass from the center to the left or right side according with the temperature homogeneity measured in the three points thermocouple gate. In the zones where we have curves or dimensions reduction of the channel, the combustion system of the single zone is controlled in a separated way and we can control: left and right side of combustion system and the central cooling of the same zone.

  

Recuperative Continuous Furnace 10 to 80 tons/ day Falorni proposal

This short presentation is necessary to explain the type of experience that we have in the field of big plants construction.
The aim of Falorni Company is to start to cooperate with big containers and tableware producers on the basis of the long time experience that we have in the Italian glass containers market.

The list of accessories, services and complete plant we can supply is the follows:

• Thermocouple R – S – B Type standard and special shape with different coating and a big range of compensating cables.
• Gas Burners and accessories for End-fired regenerative furnace and for side-fire recuperative furnaces.
• Refractories and insulating materials for spare parts and special hot repair.
• Batch charging machine with oscillating – rotating system till 460 ton/24h capacity, covered inside with very hard wear protection.
• Stirrer mechanism systems, for forehearths elimination of the cords.
• Electric drain nozzle for high temperature constant draining of the heavy glass from the bottom of the forehearth.
• Automatic combustion and control system for melting tank regenerative and recuperative continuous furnaces.
• Regenerator reversal system.
• Air jet damper.
• Automatic combustion and control system for forehearths.
• Glass level control systems.
• Heat Steel tube bundle recuperator for pre-heating of the air till 750°C.
• Heat steel double shell recuperator for pre-heating of the air till 600°C.
• Electric boosters for: MELTING BOOSTER, BARRIER BOOSTER, THROAT BOOSTER
• Regenerative End-fired glass melting furnaces.
• Recuperative End-fired glass melting furnaces.
• Recuperative Side-fired glass melting furnaces.
• Recuperative flexible Side –fired melting furnaces.