EXAMPLES OF BEST PRACTICES – THE ENGINEERING APPROACH FOR BOILERS

Boiler Water Chemistry out of the Control Box

A plant was experiencing continual out-of-specification readings for their coordinated phosphate boiler program; that is, they were frequently “out of the box” with respect to their control range. There was no immediately obvious reason for the lack of control, and it resulted in the operators making manual adjustments to the blowdown to try to improve their control. This, in turn, resulted in periodic energy and water loss through excessive blowdown, and variation in cycles of concentration.

As there was no clear reason, and it appeared to be related to boiler cycles, plant personnel started to talk about hideout. This is a serious concern, and was important to determine the real reason for the lack of control.

The Engineering Approach, looking at best practices, was chosen for problem solving. The first thing done was to complete a mechanical survey of the boiler system, focusing on everything that could be influencing the boiler reading. The feedwater system was examined, including raw water treatment, demineralization, the demineralized water storage tanks, the condensate system, and the boiler itself. The goal was to determine if there were additional unauthorized water streams being brought into the system, whether proper pretreatment was occurring, whether there was unexpected contamination, and its source, and so forth.

Following the mechanical survey, an operational survey was performed. This involved statistical analysis of the plant’s control capability in critical control parameters such as pH, cycles, phosphate, chemical feed, conductivity, etc. This will help to explain why there is a control problem in this boiler system.

The parameters tested daily by the operators for feedwater, condensate, and boiler water were examined. The historical deaerator operation was looked at, as well as its maintenance logs. Historical data on condensate return and contaminant concentration were analyzed, as were resin replacement history, and regeneration practices.

All laboratory testing methods were reviewed including frequency, adherence to procedures, instrumentation, calibrations, test methods chosen, sample gathering, and so forth. This was done to make sure that the data being analyzed was statistically accurate, and that correct conclusions would be drawn.

Both ONDEO Nalco and plant personnel did the mechanical and operational surveys. This made sure that the systems were properly surveyed, and nothing was overlooked.

Finally, a chemical audit was done for the system to examine both the program choice, as well as the program application. This included feed location, sampling location, injection methods, etc. This data was examined separately, and in conjunction with the mechanical and operational survey results.

After examining all the data gathered from the various surveys, the conclusion was that there were no mechanical issues that were affecting the lack of control of the internal treatment. The chemical program being used was the technically correct choice given the feedwater pretreatment and water quality.

Furthermore, if operated properly, the system was in fact capable of being in control during a much larger percentage of the time than was being experienced (<50%). The operators were not taking the holding time of the boiler into account when making blowdown adjustments, and were often “chasing their tail” when trying to move the boiler parameters “into the box.” In fact, most of the problems were caused by the operators overreacting to changes in test results from the boiler water chemistry.

The boiler was experiencing frequent load swings due to plant operation. These load swings could not be evened out due to plant configuration and requirements. Surveys also showed that the manual control of the feedwater treatment products was exacerbating the problems as manual adjustments made as the load was swinging were not necessarily timely.

Actions taken to improve the situation included operator training. Training on holding time and the length of time it would take to have a change be seen gave operators a better understanding of what was going on in the boiler system. Management and the operators agreed that, except in case of emergency, blowdown rate changes would only be made on the day shift. This allowed the plant to stop exaggerating the changes.

The feedwater treatment was also automated, providing more consistent feedwater treatment, even through large load swings for the boiler. Results from this relatively simple “MOC” study were very positive. The percent of time the boiler spent “in the box” increased from <50% to >90%, and a project is in place to study whether it is possible to improve this further.

With the training, the operators understood the overall system much better. They were able to reduce the amount of reacting they did, and were much happier on the job. It also freed operators’ time for more value-added proactive projects.

Automation improved overall system operation, and resulted in feed optimization, even with fairly large swings in steam load. This, in turn, allowed a minimization of feed—no “overfeed” was required to ensure system protection.

Additional savings were realized by the plant through optimized blowdown. This reduced both water and energy usage resulting in reduction of total cost of operation for the utility department, and improved boiler operations through consistent cycles of concentration.

Through the use of the Best Practices Engineering Approach (mechanical – operational – chemical), the plant saw good returns with a small investment in time and money. The investment was for surveys and data analysis and some automation equipment. The plant was able to eliminate hideout as a possible cause for the problem, improve overall operations, and reduce overall cost of the operation through optimization of their existing systems, rather than through a reduction in chemical price/pound. There was no quantification of what the plant saved through increased reliability and extended lifetime for the boiler.

By looking at the overall operations rather than just looking for a quick band-aid, the plant was able to quickly optimize operations and save money. This resulted in a very happy customer, an optimized system, and a better partnership between the customer and ONDEO Nalco. We were seen to provide a value-added service through our on-site technical representative acting as a consultant to the customer and using our best practices— The Engineering Approach.