Today’s burner controls offer variable safety times for opening the fuel valves, enable the prepurge time to be adapted to any fan output and boiler room and use two main gas valve outputs to check the gas valve in accordance with EN 1643.
An integrated flame monitor enables the direct connection of flame sensors that are suitable for special fuels or for both standard fuels, namely gas and oil. Thanks to separate control inputs and valve outputs for gas and oil operation it is possible to change fuels even while the flame is constantly present. This can be carried out in just a few seconds, during operation, without the boiler experiencing any power loss.
A data output provides all the status data; add-on modules can be used to transmit this data over a distance of several hundred metres via fieldbus or even Industrial Ethernet.
This complexity is reflected in all applications, whether they involve single burners or interlinked plants. One requirement is always the same: the automation solution must take care of the various safety and standard control technology functions but must also be convenient and easy to operate. That’s why manufacturers like Pilz supply systems whose complexity can be adapted to suit the different applications and whose hardware and software consider the specific requirements of burner management.
Burner control must comply with current standards
Furnaces and burners are subject to special directives. EU directives for furnaces only came into existence in 2004. Before then national standards were used, which have only become established at European level in the last few years. For example, industrial thermoprocessing equipment is classified as machinery under the terms of the Machinery Directive, falling under the scope of EN 746 as the standard for "industrial thermoprocessing equipment”.
Furnaces do not belong under industrial thermoprocessing equipment, nor are they used to heat process liquids and gases in the chemical industry, so they fall under the scope of the European standard EN 50156-1 as the general standard for electrical equipment.
Today’s modern burner management requires appropriate solutions for a range of applications – and this requirement will be even greater in the future. All furnaces are equipped with special burner controls or a burner management system (BMS) as part of the safety and automation technology.
In keeping with TÜV’s safety classification, the design of the burner controls must comply with the following standards: The new international standard EN 62061, the specific burner management standard EN 50156, which is based on EN 62061, or the familiar European engineering standard EN ISO 13849.
Valve operation places demands on the hardware
Whether centralised or decentralised, the burner management system for automatic operation of the burner equipment is fully installed within special control cabinets. It monitors the safety-related functions as well as functions such as starting and stopping the plant, controlling valves and flaps and the visualisation of operating conditions and diagnostic messages.
While failsafe programmable control systems are used for larger applications, a smaller-scale safety system is sufficient for applications with a lower requirement for input and output information.
Decentralised panels can be used for visualisation, for control and to display operational and fault messages; these can be connected via standard fieldbuses or via an Ethernet system.
Due to the potential risk arising from a furnace, regulations define the requirements that safety shut-off valves must meet when used in fuel lines. As these are intended to interrupt the fuel supply immediately in the event of a fault, the approvals bodies concentrate in particular on the hardware and software used to drive the valves.
This is why Pilz has expanded its range of failsafe interfaces for use in burner management, for example. A variety of safety devices designed with diverse relays are planned; this is specified for shutting down the main fuel valve, as stated in EN 50156. These safety relays are approved for use in burner controls because of their internal diverse structure.
On interlinked plants that extend over a wide area, modular or compact programmable safety and control systems monitor both the safety-related and the standard control functions. In conjunction with a decentralised I/O system the whole I/O periphery can be implemented cost effectively, as the input and output requirement can be adapted precisely to suit the individual application. Communication interfaces to most fieldbus systems and various Ethernet systems mean that safety can quickly and easily be incorporated into the full control sequence of the relevant firing plant.
Software function blocks provide easier operation
Software, of course, plays an important role in addition to the hardware and is a key factor in defining the functionality of modern automation solutions. It also helps to reduce the complexity for the user when implementing the required safety functions. Software function blocks have been approved by TÜV and BG and also help to simplify integration by enabling safety-related control functions to be implemented quickly and easily.
Safety-related areas can be equipped with a multitude of safety devices such as E-STOP pushbuttons, safety gates or light beam devices. Safety devices are required in various quantities and combinations, depending on the functions that need to be monitored.
To control these devices and perform a range of process engineering functions, Pilz developed a modular block system (MBS) for its programmable safety and control systems, helping to save the user both time and money.
The MBS consists of individual software blocks, otherwise known as standard function blocks, which are tailored specifically towards the relevant safety device or process engineering function. Up to 600 standard function blocks can be used together in any combination. They are encoded by an authorised body so that they cannot be modified. When included within a user program, program testing can be restricted to new parts of the program, considerably reducing the test time.
Standard function blocks are also available for burner management and may be used in the safety section of a programmable safety and control system. They comply with the relevant standards and directives for burners, steam boilers and thermoprocessing equipment. The software package offers "automatic burner control system” functionality as well as additional individual functions required for burner control.
With the "automatic burner control system” it is possible to control and monitor a single oil or gas burner with one block. This block contains all the necessary functions. Potential application areas are plants equipped with a high number of relatively simple burners, such as a tunnel oven.
Functions include control and monitoring of the burner cycle, the safety, monitoring and error sequence, combustion air pressure and fuel pressure. Not to mention flame monitoring, tightness control, compound control and error reset.
