Modern Packaged Boiler Operation, Maintenance and Training
The latter part 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 provide an unsurpassed degree of reliability. The present day, micro-processor based, high-integrity, "Boiler Control System" (BCS) has the capacity to perform lots of the tasks traditionally undertaken by the qualified operator allowing extended periods of automatic operation without the human intervention whatsoever. A key feature of modern packaged boilers is they are created 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're defined in local boiler codes and standards and differ widely between jurisdictions. For instance, in a few, a high-pressure boiler means any boiler operating above 1 BAR (approximately 15 psig) pressure and, irrespective of all other considerations, it must always be beneath 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 accommodate the demand from industry for this type of boiler.
Industrial boilers of most types generally fall into one of three categories in terms of their operational and qualification requirements. They are:
? Attended Boilers;
? Limited-Attendance Boilers;
? Unattended Boilers.
What is a "packaged boiler"?
The word "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 really 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 get in touch to the steam distribution system, water, fuel, and electricity supplies. Virtually 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's an attended boiler?
Until relatively recently, almost all steam boilers operated in the "Attended" mode. That is, they were necessary 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 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 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 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 rather than 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 those that have been upgraded from attended status are classified as limited-attendance due to the fact their control systems usually do not achieve the same standards of integrity and reliability as do modern micro-processor based systems. Many also include provision for manual intervention which in most jurisdictions disqualifies them for consideration for unattended status.
What is an unattended boiler?
An Unattended Boiler is essentially a completely automatic boiler that operates beneath the continuous supervision and control of a sophisticated, 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 this type of boiler is that generally in most jurisdictions boiler codes and standards dictate 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 also if a qualified operator is available. Used, the BCS employed on an unattended boiler has no provision for manual operation. In the event of a control system fault or a potentially unsafe condition, the BCS will turn off 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 has 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. Newer 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 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 beneath 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, 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 is becoming 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 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 make sure 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 built with a minimum, specified inventory of safety equipment that will automatically shut down the boiler in case of a potentially unsafe condition.
The classification put on a particular packaged boiler depends largely on the sophistication of the BCS or, sometimes, the sort of fuel that is fired. For example, a 10 MW boiler firing natural gas may achieve unattended classification in which 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, 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 the Limited-Attendance and Unattended modes of operation are:
Limited Attendance
? An appropriately qualified operator or responsible person must be on-site at all times 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 allows for 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 must be on-site at all times that the boiler is in service and should 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 site provided that they're 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 under the control of the BCS provided that they're suitably equipped to the satisfaction of an approved inspection body;
? Unattended boilers are allowed 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 some jurisdictions. The 72H notation in Europe for instance, 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 may 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.
Get more info 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 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 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 are not a complete substitute for supervision. A measure of supervision by way of 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 which are operated in strict compliance with the manufacturer's recommendations, boiler codes and standards have an excellent safety record worldwide. Because they're made 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 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 should be a high degree of confidence in the integrity of the BCS and the routine testing procedures should therefore be regarded as a key element of safe operation.
Although those tests are usually universal in nature, there are differences within 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 deciding on this kind of boiler. Failure to meet up that obligation will usually be interpreted as a breach of OSHA regulations. If in doubt, you should seek clarification from your own boiler inspector, inspection body, the boiler manufacturer or the local regulatory authority.
Who is 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, an individual nominated by the owner to perform that role. The Controller will not necessarily have to be closely involved 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 including 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 instance, OSHA, environmental agencies, inspection bodies etc.
The Controller is normally 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 someone 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 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 required with 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 principal 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 expected to diagnose and rectify equipment or system failure. They should be competent to respond 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 really a key facet of unattended boiler operation. There were numerous recent catastrophic boiler incidents resulting from 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 typical acceptable by the manufacturer and the inspection body. They need to have a thorough understanding of the role and functionality of the BCS in relation to limited-attendance and unattended operation.
Boiler codes and regulations define minimum acceptable standards because of this role which might differ between jurisdictions. In general, 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 organization itself as the approved maintenance entity. In such cases, the organisation must fulfill 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 obtained specialist training and also 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 own field devices including all safety devices and the power input system.