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For over three decades, I was associated with boiler companies designing oil- and gas-fired custom package boilers and waste heat boilers that are in operation worldwide in chemical plants, refineries, cogeneration systems, and power plants. The boilers have been operating well and performing as predicted within the margin of measurement errors. As a specialist in thermal design of heat transfer equipment and out of interest, I would correlate field data from operating units with predicted performance to check the correction factors to be incorporated in heat transfer or gas pressure drop correlations that were used for designing the boilers. I would review operating data such as boiler exit gas temperature, steam generation, fuel input, gas pressure drop, evaporator, superheater performance, their tube wall temperatures, and other process-related parameters and compare the results with predicted data. Over the years this has helped me to fine-tune the calculation procedure and modify the correction factors used in the performance evaluation of various heat transfer surfaces. Through the publication of hundreds of articles during this period, I have also been sharing thermal design procedures for boilers and HRSGs with the engineering community. I have written a few books, the recent being Industrial Boilers and HRSGs, where the emphasis was on sizing and performance evaluation of steam generator and waste heat boiler components. For the past decade, since the publication of the cited book, I have been playing the role of a boiler consultant. The transformation from a boiler designer to a boiler consultant has been gratifying as I can interact with plant engineers worldwide and learn from them about various boiler performance issues and suggest modifications to solve boiler-related problems or improve their performance (the word boiler refers to a steam generator as well as a waste heat recovery unit). Many plant engineers or even consultants have no clue as to how a boiler should be evaluated before it is bought or what information should be obtained from boiler suppliers regarding its thermal performance aspects. They rely entirely on the sales pitch from boiler suppliers and buy it without giving any critical thought to its design from a thermal performance viewpoint. Purchasing a boiler is thought of as purchasing a commodity. When purchasing a steam generator or HRSG, plant engineers have to evaluate several factors keeping in mind that the life of a boiler is about 30 to 40 years and that the plant will have to face the consequence of any wrong decision for a long time...