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 modern, 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 the human intervention whatsoever. An integral feature of modern packaged boilers is that they are created 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 instance, in some, a high-pressure boiler means any boiler operating above 1 BAR (approximately 15 psig) pressure and, irrespective of all the 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 along with other relevant legislation have already been revised and extended to accommodate the demand from industry for this type of boiler.
Industrial boilers of most types generally belong to among three categories regarding their operational and qualification requirements. They are:
? Attended Boilers;
? Limited-Attendance Boilers;
? Unattended Boilers.
What is a "packaged boiler"?
Boiler service Middlesbrough Packaged Boiler" is used to spell it out a boiler that's factory built and delivered either fully assembled or, as pre-built modules which might 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'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 for example 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 at all times that it was 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 now an endangered species in small to mid-sized plants supplying process steam. At the minimum, their role has changed from that of direct, hands-on operation to one of supervising the operation of the BCS and performing tasks that ensure its continuing integrity and compliance with certain requirements of boiler codes and standards.
Boiler operation has evolved to the stage that in many jurisdictions, fully attended operation is unusual beyond large, complex plants. The exceptions are large power utilities, chemical recovery boilers and similar integrated processes where in fact the boiler is a key component.
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. A key 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 those which were upgraded from attended status are classified as limited-attendance simply because their control systems usually 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 in most jurisdictions disqualifies them for consideration for unattended status.
What is an unattended boiler?
An Unattended Boiler is actually a completely automatic boiler that operates beneath the continuous supervision and control of a complicated, micro-processor based, BCS. The BCS controls the complete boiler function like the energy input management system (on oil and gas-fired boilers commonly known as 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 this kind of boiler is that generally in most jurisdictions boiler codes and standards dictate that 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 in case a qualified operator can be acquired. Used, the BCS employed on an unattended boiler does not have any provision for manual operation. In case of a control system fault or a potentially unsafe condition, the BCS will turn off 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 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 info 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 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 under the continuous supervision of a qualified 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 many 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 medium sized packaged boilers from reputable manufacturers now add a high-integrity BCS as standard equipment. Where unattended operation is permitted, they may 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 achieve 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 built with a minimum, specified inventory of safety equipment which will automatically shut down the boiler in case of a potentially unsafe condition.
The classification applied to a particular packaged boiler will depend 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 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 your Limited-Attendance and Unattended modes of operation are:
Limited Attendance
? An appropriately qualified operator or responsible person should be on-site all the time 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 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 should be on-site all the time that the boiler is operating and should be immediately available if required.
Unattended
? Where unattended operation is permitted, a professional 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 achieved by a pager or cellphone signal transmitted by the BCS;
? In lots of jurisdictions, unattended boilers may start up and turn off automatically under the control of the BCS so long as they are suitably equipped to the satisfaction of an approved inspection body;
? Unattended boilers are allowed 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 some jurisdictions. The 72H notation in Europe for example, 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 beneath the control of the BCS. That's, they could only be operated in unattended mode. They could not be operated in attended mode under any circumstances even for brief periods and even in case a qualified operator is available.
Training Requirements
Boilers which are certified for unattended operation do not require 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 almost always be interpreted as a breach of Occupational Safety and Health legislation which can result in severe penalties especially if the non compliance is discovered as a result of an incident or accident.
Accident investigation reports demonstrate that the most common 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 are not 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 an excellent safety record worldwide. Because they are designed to operate unsupervised for extended periods, routine operating, maintenance and inspection requirements are generally 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 key element of safe operation.
Although those tests are usually 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 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 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 can be the owner or, a person nominated by the owner to perform that role. The Controller does not necessarily must be closely associated with hands-on, day-to-day operation but instead, 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 correct regulatory bodies for example, OSHA, environmental agencies, inspection bodies and so forth.
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.
what is a trained responsible person? - roles and responsibilities:
A "Trained Responsible Person" is someone 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, must be trained to an even 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 to have an intimate understanding 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 also 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 react to alarms, and to take appropriate action which, at the very least, ensures 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 facet of unattended boiler operation. There have been numerous recent catastrophic boiler incidents resulting from inappropriately performed maintenance tasks which in some cases, were undertaken by qualified and experienced tradesmen but, who lacked the expert understanding requirements associated with boiler maintenance.
The "Approved Maintenance Contractor" is a person or organisation with the correct skills, knowledge and experience to keep the boiler and its components to a standard acceptable by the 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 might differ between jurisdictions. Generally, they will 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 very own internal maintenance infrastructure, the Controller may apply to the inspection body to nominate the business itself as the approved maintenance entity. In such cases, the organisation must satisfy the requirement that nominated personnel performing the task have appropriate training and experience. Which will typically require that nominated workers can provide evidence of an appropriate trade qualification or, have received specialist training and have sufficient experience. Under no circumstances whatsoever should non-approved staff be permitted to perform maintenance on any pressure equipment or the BCS and its field devices including all safety devices and the power input system.