August 20, 2019
Author: E. S. Beardwood. International Water Conference 2019, Paper Number IWC 19-30. Engineers’ Society of Western Pennsylvania, https://eswp.com/water/conference-archives/
ABSTRACT: The hydrocarbon and chemical processing industries operate a large number of low and medium pressure industrial and waste heat recovery steam generators. They are typically in the 150 to 600 psig range, while some may be as high as 900 psig. For simplicity we will define medium pressure as 600 to 900 psig and low pressure less than 600 psig. As the feedwater impurity concentrations increase and cycled percent recovery of said impurities decrease in the boiler water, the potential for tube metal overheating, resulting in reduced efficiency and eventual metallurgical failure increases. Some failures can be catastrophic, while others result in very costly forced outages. The former is related to increasing the total operating cost (TOC) of the thermal process, while the later results in much higher lost opportunity costs. It is these two costs that make up the total cost of ownership (TCO) associated with the forced outage failure. Most low and medium pressure steam systems suffer from poor quality feedwaters that are associated with;
- Chemical and physical corrosion within the condensate and feedwater system.
- Condensate process inleakage
- Poorly operated:
- Thermal-mechanical deaeration equipment
- Clarification and filtration equipment
- Ion exchange equipment
An assessment method to predict a time for a scheduled outage that would be used for chemical cleaning of the generator based upon the actual operating feedwater quality is required to avoid forced outage repairs. Should feedwater impurity concentrations be inconsistent and variable, due to the nature of the upsets, then the assessment becomes somewhat difficult. Therefore, a risk-based assessment that is applied to the poor feedwater quality that can be experienced over the operating period of a steam generator would be useful. This paper will provide and discuss an assessment method to predict when to schedule a chemical cleaning of steam generators to avoid tube failures and forced outages.