Combustion in the iron and steel industry
May 2004
Valves, Actuators & Pump Control
To many people, the subject of heat in the iron and steel industry conjures the thought of vast furnaces smelting the raw ingredients to produce the iron and steel. Thudding electrodes, snaking cables carrying thousands of amps and showers of sparks complete the scene.
There are other parts of the process, which require more modest temperatures to prepare the resultant metal for the consumer. Gas fired re-heat furnaces prepare the steel for the rolling mills to produce sections and plate required by industry. Once the fabricators have turned the metal into the items ordered by their customers, heat treatment may be necessary to change the hardness to the required specification or relieve stresses caused by welding. This will require a furnace capable of raising the temperature of the article at a well-controlled rate, holding at a specific level for a period of time and then cooling, again at a predetermined profile.
For these furnaces, gas is the most favoured fuel, allowing the temperature control to be as precise as the process requires. There are many excellent controllers available on the market, which can be programmed to control the burners to achieve the required temperature profile. However, these cannot do their function accurately without the burner gas and air pipe-trains having suitable valves, which can respond appropriately to the signals generated by the controllers.
Even in these days of Profibus and other communication protocols, the 'good old' 4 to 20 mA control loop is the most likely to be found in use for burner control. In some cases, slidewire feedback is still considered to be the most reliable method. Whatever system is employed, the purpose is to control the gas and airflows, thus adjusting the heat release of the burner throughout its firing range. This 'turndown' is usually quoted by the manufacturer and is the difference between the maximum and minimum firing rates (usually expressed as a ratio). Above and below these positions, the flame becomes unstable and, at the lower end, is likely to extinguish itself.
The control of these valves can be either by a mechanical linkage, coupling the gas and air valves together, with a common actuating motor; or a 'zero governor' may be employed. This system uses an actuated butterfly valve in the combustion air supply and an impulse line taken from the controlled side and connected above the diaphragm of the zero governor (aka ratio regulator). Changes in air pressure in the impulse line open or close the gas valve accordingly.
In certain applications, required by the iron and steel industry, the atmosphere in the furnace has to be completely free of oxygen. In this instance, the burners are set to fire rich. That is, there is no free oxygen in the exhaust gases once combustion has taken place. This 'off ratio' firing needs careful control and is best achieved by using a specialised controller, such as the Fireye Nexus, which has the facility of controlling the combustion air and gas valves independently. Once configured by the commissioning engineer, the air/gas ratio is controlled to a very fine degree throughout the firing range of the burner. It is even possible to incorporate an O2 trim, which will take into account the varying oxygen levels in the atmosphere, due to prevailing weather conditions.
Further reading:
Global pumping giant ready to support hydrogen economy
Valves, Actuators & Pump Control
With abundant sunshine and wind, southern Africa is perfectly positioned to become a global powerhouse in green hydrogen production. Two key projects are already in advanced stages of development in Namibia. KSB has identified the vast potential of these types of projects in southern Africa, and through its KSB Pumps and Valves subsidiaries in Namibia and South Africa is investing heavily in bringing the right skills to the region.
Read more...
Compact valve position indicator
Emerson Automation Solutions
Valves, Actuators & Pump Control
Emerson’s new TopWorx DVR Switchbox is an entry-level addition to the DV Series of valve position indicators. It combines a durable resin enclosure, compact size, and a patented cam design that provides a reliable valve position feedback for water and wastewater systems, food and beverage production lines, and industrial utilities.
Read more...
Precision, control and performance in regulators and control valves
Valve & Automation
Valves, Actuators & Pump Control
Cashco has long been a trusted name in industrial control solutions, offering a broad range of regulators and control valves designed to meet the rigorous demands of various industries. There are two key Cashco product lines, its regulators and the Ranger QCT control valve.
Read more...
Advanced solutions for valves
Bearing Man Group t/a BMG
Valves, Actuators & Pump Control
BMG delivers state-of-the-art valve solutions to diverse industries across Africa, in collaboration with InterApp, a global leader in the design and manufacture of high-quality valves.
Read more...
ENERGYValves expands operations
Valves, Actuators & Pump Control
ENERGYValves is expanding its operations with a new facility in Cape Town. The new premises will significantly enhance the company’s capacity to serve the Cape Town market and surrounding areas.
Read more...
Revolutionising slurry management in mining operations
Valves, Actuators & Pump Control
Dynamic Fluid Control has launched the Vent-O-Mat Slurry Air Release Valve, designed to set new standards in performance and technology for the mining industry.
Read more...
Inspection system for leak detection in valves in hazardous areas
Extech Safety Systems
Valves, Actuators & Pump Control
Leaking valves in industrial plants not only lead to loss, safety risks and possible contamination and pollution, but also result in high economic costs. Therefore, valves in hazardous areas require regular proper inspection and preventive maintenance to ensure their functionality.
Read more...
High-flow solenoid valve
Emerson Automation Solutions
Valves, Actuators & Pump Control
Emerson has introduced the new ASCO Series 327C solenoid valve, which features a direct-acting, high-flow design that provides superior flow-to-power ratio. It permits high flows at minimum power levels, making it ideal for use in power plants, refineries, and chemical processing facilities.
Read more...
New system improves performance of magnetic drive pumps
Valves, Actuators & Pump Control
KSB Pumps and Valves has introduced its ground-breaking MagnoProtect system for the local petrochemical, chemical and general industry markets ,to enhance the safety and performance of its magnetic drive pumps.
Read more...
Emerson software optimises maintenance
Emerson Automation Solutions
Valves, Actuators & Pump Control
Emerson has announced the Plantweb Insight Valve Health Application, a powerful software tool that combines Fisher control valve expertise with advanced analytic algorithms. The new app makes it possible for users to visualise an entire connected fleet of valves, while prioritising actions based on the health index of each valve.
Read more...
printer friendly version