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 provide an unsurpassed level of reliability. The present day, micro-processor based, high-integrity, "Boiler Control System" (BCS) has the capacity to perform a lot 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 that they are designed to operate unsupervised for extended periods.
The amount of human supervision and operator training requirements are determined by the amount of sophistication of the "Boiler Control System" (BCS). They're defined in local boiler codes and standards and differ widely between jurisdictions. For example, in a few, a high-pressure boiler is defined as any boiler operating above 1 BAR (approximately 15 psig) pressure and, regardless of all other considerations, it must always be under 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 already been revised and extended to support the demand from industry for this type of boiler.
Industrial boilers of all types generally fall into among three categories when it comes to their operational and qualification requirements. They are:
? Attended Boilers;
? Limited-Attendance Boilers;
? Unattended Boilers.
What is a "packaged boiler"?
The word "Packaged Boiler" can be used to spell it out a boiler that's factory built and delivered either fully assembled or, as pre-built modules that may be easily assembled on site. It really is essentially a self contained unit filled with a control system and all equipment required for operation. The boiler manufacturer assumes responsibility for several components and after delivery all that's needed is is for it to be connected to the steam distribution system, water, fuel, and electricity supplies. Virtually all small and mid-sized boilers manufactured today are packaged boilers plus they could 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, 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 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 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 in fact the boiler is really 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 that they may anytime 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 were 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 in most jurisdictions disqualifies them for consideration for unattended status.
What's an unattended boiler?
An Unattended Boiler is actually a completely automatic boiler that operates under 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 commonly known as 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 kind of boiler is that generally 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 all the time that it is in service. Boiler Servicing Middlesbrough may only be operated in unattended mode. It may 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 the event 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'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 every one of the BCS inputs indicate that the boiler is in a safe condition.
The BCS has some method 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. Newer systems however, store the information in the onboard micro-processor memory for a long period. They typically record a much wider range 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 beneath 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 at the mercy of 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 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 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 attain 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 built with the very least, specified inventory of safety equipment that may 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 kind of fuel that's fired. For example, a 10 MW boiler firing gas may achieve unattended classification in which a similar 10 MW boiler from the same manufacturer but firing solid-fuel may 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 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 must 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 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 always that the boiler is in service 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 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 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 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 instance, signifies that the boiler is approved for unsupervised operation for periods as high as 72-hours;
? Boiler codes 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 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 can be acquired.
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 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 which can bring about severe penalties especially if the non compliance is discovered due to 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 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 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 styles of boilers. The BCS and its associated safety devices clearly play a key 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 must 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 in their implementation between jurisdictions. It is therefore essential that the boiler owner, controller and trained Responsible Person understand that they have a responsibility to familiarise themselves with the local codes and regulations applying to this type 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 may be the owner or, a person nominated by the dog owner to execute that role. The Controller will not necessarily need to be closely involved with hands-on, day-to-day operation but instead, to supply 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;
? Making certain 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 correct 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.
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. 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 required with an intimate understanding of boiler technology but rather, a basic degree 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 expected to diagnose and rectify equipment or system failure. They should be competent to react to alarms, also to take appropriate action which, at a minimum, ensures that the boiler is shut down safely before calling for assistance.
what is an approved maintenance contractor?:
Compliance with defined maintenance procedures is really a key aspect of unattended boiler operation. There were several recent catastrophic boiler incidents caused by inappropriately performed maintenance tasks which in some cases, were undertaken by qualified and experienced tradesmen but, who lacked the specialist knowledge requirements associated with boiler maintenance.
The "Approved Maintenance Contractor" is really a person or organisation with the correct skills, knowledge and experience to keep up 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 for this role which may differ between jurisdictions. In general, they'll require that the nominated organisation be considered a boiler manufacturer or an independent contractor approved by the manufacturer or the inspection body. In organisations which have their own internal maintenance infrastructure, the Controller may connect with the inspection body to nominate the organization itself because 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 evidence of an appropriate trade qualification or, have received 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 energy input system.