The latter area of the 20th Century saw the introduction of more stringent boiler manufacturing standards, particularly in relation to welding technology and inspection, and the evolution of digital control systems that now provide an unsurpassed level of reliability. The modern, micro-processor based, high-integrity, "Boiler Control System" (BCS) has the ability to perform many of the tasks traditionally undertaken by the qualified operator allowing extended periods of automatic operation without the human intervention whatsoever. An integral 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 determined by the level of sophistication of the "Boiler Control System" (BCS). They are defined in local boiler codes and standards and differ widely between jurisdictions. For instance, in some, a high-pressure boiler means any boiler operating above 1 BAR (approximately 15 psig) pressure and, no matter all other considerations, it must constantly be beneath the control of an appropriately qualified operator. Other jurisdictions impose capacity constraints on unsupervised operation however in many, boiler codes along with other relevant legislation have been revised and extended to support the demand from industry for this type of boiler.
Industrial boilers of most types generally fall into one of three categories when it comes 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 describe a boiler that is factory built and delivered either fully assembled or, as pre-built modules that can be easily assembled on site. It is essentially a self contained unit filled with a control system and all equipment necessary for operation. The boiler manufacturer assumes responsibility for several components and after delivery all that is required is for it to get in touch to the steam distribution system, water, fuel, and electricity supplies. Almost all small and medium sized boilers manufactured today are packaged boilers and they may be the conventional firetube or watertube type, including their derivatives or, hybrid boilers such as once-through coil and electrode boilers.
What is an attended boiler?
Until relatively recently, almost all steam boilers operated in the "Attended" mode. That is, they were required to have an appropriately qualified operator on-site and in the immediate vicinity of the boiler all the time that it had been operating. Because 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 traditional boiler attendant is becoming an endangered species in small to medium sized plants supplying process steam. At 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. A key feature of limited-attendance boilers is that they may anytime be brought under the control of an appropriately qualified operator and operated in the fully attended mode under continuous supervision.
Many older packaged boilers and the ones that have been upgraded from attended status are classified as limited-attendance due to the fact their control systems do not achieve the same standards of integrity and reliability as do modern micro-processor based systems. Many likewise incorporate provision for manual intervention which generally in most jurisdictions disqualifies them for consideration for unattended status.
What is an unattended boiler?
An Unattended Boiler is actually a fully automatic boiler that operates beneath the continuous supervision and control of a complicated, micro-processor based, BCS. The BCS controls the entire boiler function like 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 security alarm, the pressure controls, trip devices, all instruments and circuitry.
A key feature of the type of boiler is that in most jurisdictions boiler codes and standards dictate a boiler that's classified as unattended should be beneath the continuous supervision and control of the BCS constantly that it is in service. The unattended boiler may only be operated in unattended mode. It could not be operated in attended mode under any circumstances even for brief periods and even if a qualified operator is available. Used, the BCS employed on an unattended boiler has no provision for manual operation. In case of a control system fault or perhaps a potentially unsafe condition, the BCS will shut down the boiler and lock-out the energy input system. It will 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 of the BCS inputs indicate that the boiler is in a safe condition.
The BCS has some means of recording all major events that cause the alarms to activate. On early unattended boilers this is typically a straightforward printer that recorded such events on a line-by-line basis. More modern systems however, store the info in the onboard micro-processor memory for a long period. They typically record a much wider range of information to provide improved oversight of boiler performance and, are sometimes integrated with a plant-wide information system which facilitates the remote storage of data for extended periods.
The unattended boiler is a relatively recent phenomenon. Traditionally most boiler installations operated under the continuous supervision of a qualified operator although in many jurisdictions, some small boilers were permitted to operate in limited-attendance mode. Until very recently, generally in most jurisdictions unattended boiler operation was subject to strict constraints. Typically, permissible maximum operating pressure and design output were severely limited and in lots of locations those constraints still apply, at least on paper. Recently however, boiler codes and standards in lots of jurisdictions have been extended to accommodate this sort 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 in recent years 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 add a high-integrity BCS as standard equipment. Where unattended operation is permitted, they could only require inspection and operational certification by an accredited inspection body to ensure compliance with National and local standards.
Limited-Attendance vs Unattended Operation
To attain 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 may 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 example, 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 those with 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 your Limited-Attendance and Unattended modes of operation are:
Limited Attendance
? An appropriately qualified operator or responsible person must be on-site always 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 rather than continuous supervision;
? Limited-Attendance boilers may anytime be brought under the control of an appropriately qualified operator and operated in the fully attended mode under continuous supervision;
? The operator or responsible person should be on-site all the time that the boiler is in service and must be immediately available if required.
Unattended
? Where unattended operation is permitted, a qualified operator isn't 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 they're available to respond to boiler outages. That's usually attained by a pager or cellphone signal transmitted by the BCS;
? In many jurisdictions, unattended boilers may begin up and turn off automatically beneath the control of the BCS provided that 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 seen that period extended in a few jurisdictions. The 72H notation in Europe for example, signifies that the boiler is approved for unsupervised operation for periods of up to 72-hours;
? Boiler codes generally in most jurisdictions specifically forbid the provision for manual intervention in the operation of unattended boilers. They must always be under the control of the BCS. That is, they could only be operated in unattended mode. They could not be operated in attended mode under any circumstances even for brief periods and also if a qualified operator can be acquired.
Training Requirements
Boilers which are certified for unattended operation do not need a qualified operator. This relaxation of the manning requirements imposes substantial obligations on boiler owners, controllers, manufacturers and inspection bodies to make sure compliance with boiler codes and 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 that may result in severe penalties especially if the non compliance is discovered due to 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 are not a complete substitute for supervision. A way of measuring 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 that are operated in strict compliance with the manufacturer's recommendations, boiler codes and standards have a fantastic safety record worldwide. Because they are made 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 associated safety devices clearly play an integral role in the safe operation of the type of boiler and so 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 key element of safe operation.
Although those tests are generally universal in nature, you can find differences within their implementation between jurisdictions. Hence, it is very important that the boiler owner, controller and trained Responsible Person recognize that they have a responsibility to familiarise themselves with the neighborhood codes and regulations applying to this kind of boiler. Failure to meet 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 neighborhood 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 execute that role. The Controller will not necessarily must be closely involved 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 https://tsboilerservicing.co.uk/ 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 an excellent Management System (QMS);
? The implementation and maintenance of appropriate safety and environmental procedures and, communications with the appropriate regulatory bodies for instance, OSHA, environmental agencies, inspection bodies and so forth.
The Controller is typically 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 hold a formal qualification such as a certificate of competency but, should be trained to a level specified by the boiler manufacturer or, to an even acceptable by an inspection body or other appropriate regulatory authority. The Responsible Person is not required to have an intimate understanding of boiler technology but instead, a basic degree of knowledge and a knowledge 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 all control and alarm systems are functioning correctly also to ensure compliance with the routine testing procedures specified in the relevant code or standard and, by the boiler manufacturer. The Responsible Person shouldn't 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 shut down safely before calling for assistance.
what's an approved maintenance contractor?:
Compliance with defined maintenance procedures is a key aspect of unattended boiler operation. There have been numerous 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 a person or organisation with the correct 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. In general, 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 own internal maintenance infrastructure, the Controller may apply to the inspection body to nominate the business itself because the approved maintenance entity. In such instances, the organisation must satisfy the requirement that nominated personnel performing the task have appropriate training and experience. That will typically require that nominated workers can provide proof a proper trade qualification or, have received specialist training and have sufficient experience. For no reason whatsoever should non-approved staff be allowed to perform maintenance on any pressure equipment or the BCS and its field devices including all safety devices and the energy input system.
