Looking back over the past 25 years it is amazing to see the technological advances that have been made in the area of boiler control. And technology, being one of the main drivers of productivity improvement, has also managed to do its thing in this specific field.
When I started off with boilers, combustion control was still carried out with what we called electro-mechanical control systems, utilizing dampers, links and electrical and mechanical devices to automatically regulate the combustion process in accordance with steam demand. This was a most basic automated control system, which one can call Level 1 automation, i.e. one notch up from manual operation.
With the advent of frequency inverters (VSD’s) and more advanced electronics the electro-mechanical controls were gradually being phased out and replaced with more advanced control systems, providing for more accurate control of air-fuel ratio and subsequent higher efficiencies and fuel savings, generally ranging between 8% and 15%. Here too one can distinguish two levels of automation.
- At the bottom end one finds a control system consisting of VSD’s, a few electronic transducers (e.g. steam pressure), controllers and typically a pressure differential switch to control the FD fan (furnace pressure). The air-fuel ratio is adjusted by means of a potentiometer which adds gain to the speed command of the stoker. Very basic, but effective and generally improving the efficiency of steam production. With a well trained operator and good supervision these systems are simple to operate and able to produce fairly good efficiencies. One can refer to these as Level 2 automation systems.
- At the top end one typically finds a control system with more advanced electronics, more instrumentation, a plc and HMI, and most probably oxygen trim control to absolutely fine tune air-fuel ratio on a continuous basis under all demand conditions. These systems are typically 2% to 3% more efficient than Level 2 systems, and often provide the ability of computation, control of complex processes, data capture and processing, information management and live boiler monitoring. We refer to these as Level 3 automation systems. And typically they would come with a higher price tag than Level 2 systems.
The challenge facing many users of steam boilers is to decide on the level of automation they should opt for. Naturally everybody would like to have a Level 3 control system for the sake of improved boiler operation and higher efficiency; however there are a number of factors to consider when making an educated decision:
- With business conditions becoming tougher and more competitive every day, there is increased pressure on management to employ technology at their disposal to the utmost, including the recording and processing of information, and even to monitor plant in operation. It saves time and improves the integrity of information and decision making, and these features alone can offset the premium of owning a Level 3 system by far. However, if a business is not committed to continuous improvement, or actively managing steam plant performance, they may be wasting good money on a Level 3 control system.
- Level 3 control systems may create the impression that they are complex to set up, to adjust and to operate. This is specifically true where operators are not adequately equipped to understand the requirements for efficient boiler operation. On many occasions however, I find the problem is with supervisory and managerial personnel that are at a loss as to the basic principles of combustion and boiler control, and the potential value the control system can add in terms of processed data and efficiency related information.
- And lastly of course the more expensive system must be financially justifiable. A large steam user may find that the additional fuel cost savings brought about by a Level 3 control system pay back the additional cost of the more advanced technology within single months. With lower steam usage it may be financially more attractive to employ a Level 2 system, unless the boiler management features offered by the Level 3 system takes preference.
Thus the question of the correct automation technology level hinges on four factors:
- The budget
- The technological and operational knowledge base
- The management culture
- The return on investment.
This post was compiled by René le Roux for Le Roux Combustion, all rights reserved. Do you want to know more about boiler control systems, or boiler optimization? Please contact us for your professional boiler automation, steam system efficiency and coal characterization needs.
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