The assessment team will need to review the available information and determine or confirm the assessment scope, boundary and level of assessment required. Three levels of assessment may be appropriate depending on the situation. A level 1 assessment is a qualitative review or paper audit. A level 2 assessment is a quantitative review based on steady-state operating conditions requiring limited infield measurements. A level 3 assessment is a quantitative review of a variable system that requires measuring data over a time span long enough to characterize the various operating conditions.
In systems with little or no variability, a level 2 assessment may be used to determine savings potential and optimization recommendation. In this level of assessment, the team will gather the appropriate data taken from plant information systems or by using portable measuring devices, giving a snapshot of conditions at the time of measurement.
In varying systems with high priority, a level 3 assessment may be used. In this level of assessment, a more complex investigation is conducted over an extended period of time sufficient to develop a system load profile. More extensive use of monitoring and a more complex data analysis are associated with this level of assessment. Detailed component failure analysis and/or hydraulic system modeling is often part of these assessments.
For example, if unexpected bearing failures are an issue, a detailed analysis of the bearing temperature in combination with system operating conditions along with an inspection of the failed bearings may be required. Image 3 shows a trend of bearing temperatures for a boiler feed pump prior to unexpected failures that was gathered from plant historical data as part of a level 3 assessment (see page 78). Once the appropriate field data is gathered, it is analyzed and optimization opportunities are identified.
Performance improvements generally fall into five categories: eliminate unnecessary uses, improve operations and maintenance practices, improve piping configuration, consider alternative pump configurations or design improvements and change pump control. An unnecessary use is putting more energy into the system than is required to meet the design. For example, operating a pump in recycle when no demand is needed, or running two pumps when only one is needed. You may need to improve operating procedures and improve controls to eliminate unnecessary use. It is important to have proper operating procedures so that pumps can be reliably switched and so that components of the pump do not fail. The assessment team needs to ensure proper procedures are in place and they are being followed.
Improving piping configuration is another method to improve performance since piping velocity is proportional to energy consumption. For existing installations, it is typically not practical to justify larger pipe; however, it should be considered and optimized for new installations. Suction piping is of utmost importance to ensure pump reliability. Make sure that installations are in compliance with industry standards ANSI/HI 9.6.6 Rotodynamic Pumps for Pump Piping and 9.8 Rotodynamic Pumps for Pump Intake Design and the net positive suction head (NPSH) margin is in accordance with ANSI/HI 9.6.1 Rotodyanmic Pumps – Guidelines for NPSH margin.
Considering alternative pump system configurations is another option to improve performance. Depending on the fluid being pumped, replacing a currently installed centrifugal pump with a positive displacement pump may be warranted. Using smaller sized pumps or installing multiple pumps in parallel or series along with trimming or installing new impellers may improve system performance.
Using proper control of the system, such as level, temperature, pressure and flow controls, is one of the most important considerations to ensure the system demand is met and the system operates optimally.
Another option is implementing variable speed control, which reduces the speed based on a feedback (such as pressure or level) to meet demand, reduces mechanical stresses, and allows for soft starting and stopping.
Energy savings are important, but as mentioned previously, in many cases the nonenergy benefits outweigh the energy benefits. Some of these nonenergy benefits include higher reliability, increased productivity, less equipment wear and tear, reduced maintenance costs, reduced production losses, increased capacity utilization, reduced environmental impact and improved safety.
Most of the time, a system assessment is conducted because of failures or reliability issues. Recommendations in the assessment report should address these issues and calculate life cycle cost impacts. It is important to economically validate the optimization opportunities.
Once an assessment is completed, the results should be documented and reported to the management team. The report and other documentation delivered with the report should include sufficient raw data from the assessment so that the analyses performed can be confirmed by a third party. This documentation should be structured so it can be easily accessed by verifiers and other people not involved in its development.