The latter area of the 20th Century saw the introduction of more stringent boiler manufacturing standards, particularly with regards to welding technology and inspection, and the evolution of digital control systems that now offer an unsurpassed level of reliability. The modern, micro-processor based, high-integrity, "Boiler Control System" (BCS) has the ability to perform most of the tasks traditionally undertaken by the qualified operator allowing extended periods of automatic operation without any human intervention whatsoever. A key feature of modern packaged boilers is they are made to operate unsupervised for extended periods.
The amount of human supervision and operator training requirements are dependant on the amount of sophistication of the "Boiler Control System" (BCS). They are defined in local boiler codes and standards and differ widely between jurisdictions. For example, in a few, a high-pressure boiler means any boiler operating above 1 BAR (approximately 15 psig) pressure and, no matter all other considerations, it must at all times be under the control of an appropriately qualified operator. Other jurisdictions impose capacity constraints on unsupervised operation however in many, boiler codes and other relevant legislation have been revised and extended to support the demand from industry because of this type of boiler.
Industrial boilers of all types generally belong to one of three categories with regards to their operational and qualification requirements. They're:
? Attended Boilers;
? Limited-Attendance Boilers;
? Unattended Boilers.
What is a "packaged boiler"?
The term "Packaged Boiler" is used to spell it out a boiler that is factory built and delivered either fully assembled or, as pre-built modules that can be easily assembled on site. It really is essentially a self contained unit filled with a control system and all equipment necessary for operation. The boiler manufacturer assumes responsibility for all components and after delivery all that's needed is is for this to be connected to the steam distribution system, water, fuel, and electricity supplies. Almost all small and mid-sized boilers manufactured today are packaged boilers plus they may be the conventional firetube or watertube type, including their derivatives or, hybrid boilers such as once-through coil and electrode boilers.
What's an attended boiler?
Until relatively recently, almost all steam boilers operated in the "Attended" mode. That's, they were required to have an appropriately qualified operator on-site and in the immediate vicinity of the boiler constantly that it was operating. Since the introduction of micro-processor based technology to boilers from around 1990 onwards, many traditional attended boiler owners have upgraded their control systems. Given also that micro-processor based controls are actually an almost universal feature on new packaged-boilers, the original boiler attendant is becoming an endangered species in small to medium sized plants supplying process steam. At the very least, their role has changed from that of direct, hands-on operation to 1 of supervising the operation of the BCS and performing tasks that ensure its continuing integrity and compliance with the requirements of boiler codes and standards.
Boiler operation has evolved to the point that in many jurisdictions, fully attended operation is unusual outside of large, complex plants. The exceptions are large power utilities, chemical recovery boilers and similar integrated processes where the boiler is really a key component.
exactly what is a limited-attendance boiler?
The Limited-Attendance mode of operation allows for periodic checking of the boiler at set minimum intervals instead of continuous attendance. An integral feature of limited-attendance boilers is they may at any time be brought beneath the control of an appropriately qualified operator and operated in the fully attended mode under continuous supervision.
Many older packaged boilers and the ones which have been upgraded from attended status are classified as limited-attendance simply because their control systems usually do not achieve exactly the same standards of integrity and reliability as do modern micro-processor based systems. Many likewise incorporate provision for manual intervention which in most jurisdictions disqualifies them for consideration for unattended status.
What's an unattended boiler?
An Unattended Boiler is essentially a fully automatic boiler that operates beneath the continuous supervision and control of a sophisticated, micro-processor based, BCS. The BCS controls the entire boiler function including the energy input management system (on oil and gas-fired boilers often called the "Burner Management System" or, BMS), the water level management system, the alarm system, the pressure controls, trip devices, all instruments and circuitry.
A key feature of the kind of boiler is that in most jurisdictions boiler codes and standards dictate that a boiler that is classified as unattended should be under the continuous supervision and control of the BCS always that it is operating. The unattended boiler may only be operated in unattended mode. It may not be operated in attended mode under any circumstances even for brief periods and even if a qualified operator can be acquired. In practice, the BCS employed on an unattended boiler has no provision for manual operation. In the event of a control system fault or perhaps a potentially unsafe condition, the BCS will shut down the boiler and lock-out the power input system. It'll prevent a boiler restart until such time that the control system fault has been repaired or, the potentially unsafe condition has been addressed and all the BCS inputs indicate that the boiler is in a safe condition.
The BCS is equipped with some means of recording all major events that cause the alarms to activate. On early unattended boilers this was typically a simple printer that recorded such events on a line-by-line basis. More modern systems however, store the information in the onboard micro-processor memory for a long period. They typically record a much wider selection of information to provide improved oversight of boiler performance and, are occasionally integrated with a plant-wide information system which facilitates the remote storage of data for extended periods.
The unattended boiler is really a relatively recent phenomenon. Traditionally most boiler installations operated beneath the continuous supervision of a professional operator although in many jurisdictions, some small boilers were permitted to use in limited-attendance mode. Until very recently, generally in most jurisdictions unattended boiler operation was at the mercy of strict constraints. Typically, permissible maximum operating pressure and design output were severely limited and in lots of locations those constraints still apply, at the very least on paper. In recent years however, boiler codes and standards in many jurisdictions have already been extended to accommodate this kind of boiler and in others it has become quite common for local regulatory authorities to grant exemptions on a case-by-case basis.
With the advent recently of improved manufacturing standards and the rapid evolution of sophisticated, increasingly reliable micro-processor based control and monitoring systems, most small to mid-sized packaged boilers from reputable manufacturers now incorporate a high-integrity BCS as standard equipment. Where unattended operation is permitted, they could only require inspection and operational certification by a certified inspection body to ensure compliance with National and local standards.
Limited-Attendance vs Unattended Operation
To accomplish Limited-Attendance or Unattended classification, the boiler is subject to strict statutory oversight covering operation, maintenance, servicing and record keeping. Boiler codes and standards require that boilers in either category be equipped with a minimum, specified inventory of safety equipment that will automatically shut down the boiler in case of a potentially unsafe condition.
The classification applied to a specific packaged boiler depends largely on the sophistication of the BCS or, sometimes, the type of fuel that's fired. For instance, a 10 MW boiler firing natural gas may achieve unattended classification where a similar 10 MW boiler from exactly the same manufacturer but firing solid-fuel could be classified as limited-attendance. Firing solid-fuels, particularly people that have a variable moisture content, may also be something of a black-art requiring a qualification of skill and experience. In this author's jurisdiction, unattended solid-fuel boilers are nevertheless not unusual even for quite large boilers over 20 MW capacity and frequently in multiple boiler installations.
The key differences between the Limited-Attendance and Unattended modes of operation are:
Limited Attendance
? An appropriately qualified operator or responsible person should be on-site at all times that the boiler is operating;
? Codes and standards usually require that the boiler be continuously supervised during startup and shutdown periods;
? During normal operation, the limited-attendance mode permits periodic checking of the boiler at set minimum intervals instead of continuous supervision;
? Limited-Attendance boilers may at any time be brought beneath the control of an appropriately qualified operator and operated in the fully attended mode under continuous supervision;
? The operator or responsible person must be on-site constantly that the boiler is in service and must be immediately available if required.
Unattended
? Where unattended operation is permitted, a qualified operator is not a mandatory requirement. The boiler may be supervised by an appropriately trained "Responsible Person";
? The operator or responsible person may leave the website provided that he or she is available to react to boiler outages. That's usually achieved by a pager or cellphone signal transmitted by the BCS;
? In many jurisdictions, unattended boilers may start up and shut down automatically beneath the control of the BCS so long as they're suitably equipped to the satisfaction of an approved inspection body;
? Unattended boilers are permitted to operate unsupervised for extended periods and generally in most jurisdictions this is currently 24-hours. Recent control and monitoring systems innovations by some manufacturers however, have observed that period extended in some jurisdictions. The 72H notation in Europe for instance, signifies that the boiler is approved for unsupervised operation for periods as high as 72-hours;
? Boiler codes generally in most jurisdictions specifically forbid the provision for manual intervention in the operation of unattended boilers. They need to all the time be under the control of the BCS. That is, they may only be operated in unattended mode. They may not be operated in attended mode under any circumstances even for brief periods and also if a qualified operator is available.
Training Requirements
Boilers which are certified for unattended operation usually do not require a qualified operator. This relaxation of the manning requirements imposes substantial obligations on boiler owners, controllers, manufacturers and inspection bodies to ensure compliance with boiler codes along with other relevant legislation and, that boiler supervisory and maintenance staff receive adequate training. Non compliance will almost always be interpreted as a breach of Occupational Safety and Health legislation which can bring about severe penalties especially if the non compliance is discovered because of an incident or accident.
Accident investigation reports demonstrate that the most frequent contributing causes to boiler accidents are operator intervention with the safety controls, inadequate maintenance, device failure following maintenance by unqualified personnel, isolation or deliberate disablement of the safety devices, inappropriate operating practices and inadequate water treatment. Automatic controls aren't a complete substitute for supervision. A measure of supervision by way of a qualified operator or perhaps a trained Responsible Person familiar with the BCS and the operation of the boiler plant is an essential feature of safe operation.
Unattended boilers which are operated in strict compliance with the manufacturer's recommendations, boiler codes and standards have a fantastic safety record worldwide. Because they're designed to operate unsupervised for extended periods, routine operating, maintenance and inspection requirements are usually more stringent than for other types of boilers. The BCS and its own associated safety devices clearly play a key role in the safe operation of the type of boiler and are therefore subject to strict compliance with routine testing procedures by the trained Responsible Person and the approved maintenance contractor. It is extremely important that there should be a high level of confidence in the integrity of the BCS and the routine testing procedures should therefore be seen as a important element of safe operation.
Although those tests are generally universal in nature, there are differences in their implementation between jurisdictions. Hence, it is very important that the boiler owner, controller and trained Responsible Person understand that they will have a responsibility to familiarise themselves with the local codes and regulations deciding on this sort of boiler. Failure to meet up that obligation will most likely be interpreted as a breach of OSHA regulations. If in doubt, you need to seek clarification from your boiler inspector, inspection body, the boiler manufacturer or the local regulatory authority.
Who's the boiler controller? - roles and responsibilities:
Boiler codes and standards generally require that unattended boiler installations have a nominated "Controller". This may be the owner or, an individual nominated by the dog owner to perform that role. The Controller does not necessarily must be closely associated with hands-on, day-to-day operation but rather, to provide general oversight of the boiler operation and maintenance.
The Controller's responsibilities include:
? Ensuring compliance with the Boiler code or relevant standard like the maintenance of appropriate operational and engineering records;
? Ensuring that the boiler is supervised by appropriately qualified or trained persons;
? The implementation and maintenance of a Quality Management System (QMS);
? The implementation and maintenance of appropriate safety and environmental procedures and, communications with the appropriate regulatory bodies for example, OSHA, environmental agencies, inspection bodies etc.
The Controller is normally a engineering, maintenance or departmental manager or, someone in the organization that holds a qualification or Certificate of Competency in boiler operation.
exactly what is a trained responsible person? - roles and responsibilities:
A "Trained Responsible Person" is a person who is appointed by the controller to exercise day-to-day supervision of the boiler. He or she is not required to carry a formal qualification for instance a certificate of competency but, must be trained to a level specified by the boiler manufacturer or, to a level acceptable by an inspection body or other appropriate regulatory authority. The Responsible Person is not required with an intimate knowledge of boiler technology but instead, a basic level of knowledge and an understanding of the functionality and roles of the boiler components, mountings and ancillary systems like the fuel, feedwater, and steam distribution systems.
The primary roles of the Responsible Person are to exercise general day-to-day supervision of the boiler operation, verify that control and alarm systems are functioning correctly and to ensure compliance with the routine testing procedures specified in the relevant code or standard and, by the boiler manufacturer. The Responsible Person should not necessarily be likely to diagnose and rectify equipment or system failure. They should be competent to respond to alarms, also to take appropriate action which, at the very least, means that the boiler is turn off safely before calling for assistance.
what is an approved maintenance contractor?:
Compliance with defined maintenance procedures is a key facet of unattended boiler operation. There have been many recent catastrophic boiler incidents caused by inappropriately performed maintenance tasks which in some instances, were undertaken by qualified and experienced tradesmen but, who lacked the expert understanding requirements connected with boiler maintenance.
The "Approved Maintenance Contractor" is really a person or organisation with the appropriate skills, knowledge and experience to maintain the boiler and its components to a standard acceptable by the product manufacturer and the inspection body. They need to have a thorough understanding of the role and functionality of the BCS with regards to limited-attendance and unattended operation.
Boiler codes and regulations define minimum acceptable standards for this role which might differ between jurisdictions. Generally, they'll require that the nominated organisation be considered a boiler manufacturer or an unbiased contractor approved by the manufacturer or the inspection body. In organisations that have their very own internal maintenance infrastructure, the Controller may connect with the inspection body to nominate the organization itself as the approved maintenance entity. In such instances, the organisation must fulfill the requirement that nominated personnel performing the task have appropriate training and experience. Which will typically require that nominated workers can provide proof an appropriate trade qualification or, have obtained specialist training and have sufficient experience. Under https://www.scsplumbingandheating.co.uk/ whatsoever should non-approved staff be allowed to perform maintenance on any pressure equipment or the BCS and its own field devices including all safety devices and the power input system.