The latter part 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 degree of reliability. The present day, micro-processor based, high-integrity, "Boiler Control System" (BCS) has the capacity to perform many of the tasks traditionally undertaken by the qualified operator allowing extended periods of automatic operation without any human intervention whatsoever. An integral feature of modern packaged boilers is that they are designed to operate unsupervised for extended periods.
The degree of human supervision and operator training requirements are determined by 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 instance, in some, a high-pressure boiler is defined as any boiler operating above 1 BAR (approximately 15 psig) pressure and, regardless of all the considerations, it must always be beneath the control of an appropriately qualified operator. Other jurisdictions impose capacity constraints on unsupervised operation but in many, boiler codes along with other relevant legislation have been revised and extended to accommodate the demand from industry because of this type of boiler.
Industrial boilers of all types generally belong to among three categories with regards to their operational and qualification requirements. They're:
? Attended Boilers;
? Limited-Attendance Boilers;
? Unattended Boilers.
Exactly 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 could be easily assembled on site. It is essentially a self contained unit complete with a control system and all equipment necessary for operation. The boiler manufacturer assumes responsibility for all components and after delivery all that is required is for this to be connected to the steam distribution system, water, fuel, and electricity supplies. Virtually all small and medium sized boilers manufactured today are packaged boilers and they could be the conventional firetube or watertube type, including their derivatives or, hybrid boilers such as for example once-through coil and electrode boilers.
What is an attended boiler?
Until relatively recently, the vast majority of steam boilers operated in the "Attended" mode. That's, they were necessary to have an appropriately qualified operator on-site and in the immediate vicinity of the boiler constantly 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 now 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 the minimum, 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 stage that in lots of jurisdictions, fully attended operation is unusual beyond 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 permits 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 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 which were upgraded from attended status are classified as limited-attendance due to the fact their control systems 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 generally in most jurisdictions disqualifies them for consideration for unattended status.
What's an unattended boiler?
An Unattended Boiler is actually a fully automatic boiler that operates under the continuous supervision and control of a sophisticated, micro-processor based, BCS. The BCS controls the complete 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 this kind of boiler is that generally in most jurisdictions boiler codes and standards dictate a boiler that is classified as unattended must be under the continuous supervision and control of the BCS at all times that it is in service. The unattended boiler may only be operated in unattended mode. https://www.scsplumbingandheating.co.uk/ could not be operated in attended mode under any circumstances even for brief periods and also in case a qualified operator is available. Used, the BCS employed on an unattended boiler does not have any provision for manual operation. In the event of a control system fault or a potentially unsafe condition, the BCS will shut down the boiler and lock-out the power 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 every one 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 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 an extended period. They typically record a much wider selection of information to supply 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 really a relatively recent phenomenon. Traditionally most boiler installations operated beneath the continuous supervision of a professional operator although in lots of jurisdictions, some small boilers were permitted to use 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 many locations those constraints still apply, at the very least on paper. In recent years however, boiler codes and standards in lots of jurisdictions have been extended to accommodate this type 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 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 at the mercy of 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 which will automatically turn off the boiler in case of a potentially unsafe condition.
The classification put on a specific packaged boiler depends largely on the sophistication of the BCS or, sometimes, the sort of fuel that is 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 may be classified as limited-attendance. Firing solid-fuels, particularly those with a variable moisture content, is sometimes something of a black-art requiring a degree 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 should be on-site constantly that the boiler is in service;
? 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 under 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 at all times that the boiler is operating and must be immediately available if required.
Unattended
? Where unattended operation is permitted, a qualified operator is not a mandatory requirement. The boiler could be supervised by an appropriately trained "Responsible Person";
? The operator or responsible person may leave the site provided that they're available to react to boiler outages. That is usually achieved by a pager or cellphone signal transmitted by the BCS;
? In lots of jurisdictions, unattended boilers may begin 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 in most jurisdictions that 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 in most jurisdictions specifically forbid the provision for manual intervention in the operation of unattended boilers. They need to always be beneath 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 in case a qualified operator can be acquired.
Training Requirements
Boilers which are certified for unattended operation usually 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 along with other relevant legislation and, that boiler supervisory and maintenance staff receive adequate training. Non compliance will more often than not be interpreted as a breach of Occupational Safety and Health legislation that may bring about severe penalties particularly if the non compliance is discovered as a result 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, control 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 way of measuring supervision by a qualified operator or a trained Responsible Person familiar with the BCS and the operation of the boiler plant can be 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 designed to operate unsupervised for extended periods, routine operating, maintenance and inspection requirements are usually more stringent than for other styles of boilers. The BCS and its associated safety devices clearly play a key role in the safe operation of this type of boiler and are therefore at the mercy of strict compliance with routine testing procedures by the trained Responsible Person and the approved maintenance contractor. It is extremely important that there must be a high degree 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 in their implementation between jurisdictions. It is therefore essential 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 type of boiler. Failure to meet up that obligation will usually be interpreted as a breach of OSHA regulations. If in doubt, you need to seek clarification from your own 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, a person nominated by the owner to execute 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 including the maintenance of appropriate operational and engineering records;
? Making certain 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 correct regulatory bodies for example, OSHA, environmental agencies, inspection bodies and so forth.
The Controller is typically a engineering, maintenance or departmental manager or, someone in the business that holds a qualification or Certificate of Competency in boiler operation.
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. They're not required to carry a formal qualification like 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 needed with an intimate understanding of boiler technology but rather, a basic degree of knowledge and a knowledge of the functionality and roles of the boiler components, mountings and ancillary systems including the fuel, feedwater, and steam distribution systems.
The principal 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 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 expected to diagnose and rectify equipment or system failure. They must be competent to respond to alarms, and to take appropriate action which, at the very least, ensures that the boiler is turn off 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 were several 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 associated with boiler maintenance.
The "Approved Maintenance Contractor" is really a person or organisation with the correct skills, knowledge and experience to maintain the boiler and its own 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 because of this role which may differ between jurisdictions. Generally, they'll require that the nominated organisation be considered a boiler manufacturer or an independent contractor approved by the product 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 organization itself as the approved maintenance entity. In such instances, the organisation must fulfill the requirement that nominated personnel performing the work have appropriate training and experience. That will typically require that nominated staff members can provide proof a proper trade qualification or, have obtained specialist training and also have sufficient experience. Under no circumstances 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 power input system.