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This Fluid Sealing Association Knowledge Series training presentation introduces the Lifecycle cost calculator (LCC) for pump shaft seals. A description is provided on:
▪ The LCC as a decision support tool
▪ Elements that form various costs
▪ Description of the calculated outputs
▪ Worked example
The LCC – A Decision Support Tool
The shaft sealing solution to many pumping applications often have multiple solutions to choose from.
First approach may be to select the lowest up front cost solution, however, there are many more factors that should be considered.
To assist in the decision process, the Life Cycle Cost (LCC) calculator enables the quick and easy comparison of various solutions and determine which will have the lowest cost over the life of the pump.
LCC Considerations
LCC calculation tool allows the ability to compare additional considerations when selecting a shaft sealing solution:
▪ Up-front or one-time costs – costs to purchase the shaft sealing system
▪ Operating costs - costs associated with the consumption of utilities needed to support the shaft sealing system
▪ Equipment Maintenance and Repair Cost - collateral costs associated with repairs and replacement parts on the pump due to shaft seal failure
▪ Seal Maintenance and Repair Cost - costs associated with the reconditioning of the mechanical seal or the replacement of the packing rings, lantern ring, and sleeve
LCC Considerations
▪ Downtime and Loss of Production Cost - the cost of lost production resulting from unexpected seal failure
▪ Environmental Cost - cost of complying with environmental regulations
▪ Energy Cost - frictional power consumed by the shaft seal together with pump heat soak and energy consumed in additional downstream processing
Many of these are parasitic losses that are often overlooked and ignored but can contribute significantly to the operating costs of the sealing solution. The LCC calculation tool can calculate these losses using standard engineering calculations and user input.
LCC Considerations
Combining the one-time costs together with the total annual operating costs, the LCC calculation tool can calculate an expected total life cycle cost based on the projected life expectancy of a particular pumping asset.
Additionally, the LCC calculation tool provides an output of the energy that a particular sealing system consumes together with a carbon footprint in the form of “equivalent carbon dioxide emissions per year”.
Example Calculation using the LCC
Consider a typical service encountered at an oil refinery that is pumping a hot hydrocarbon fluid at 650°F (345°C). For this type of service we can compare (3) potential candidate sealing solutions to each other:
▪ Scenario 1) Single seal with API-Plan 23 (heat exchanger cooling the seal chamber).
▪ Scenario 2) Single seal with API-Plan 32 (external injection of a clean fluid into the seal chamber).
▪ Scenario 3) Dual pressurized seal with API-Plan 54 (Closed loop barrier fluid circulating system).
Example Arrangements
Scenario 1
Scenario 2
Modifying the LCC Inputs
Using the default values in the LCC calculation tool and making some minor adjustments for this example, a quick comparison can be made. Users have the ability to customize as many inputs as needed to represent their specific pump and process conditions.
To better represent the sealing solutions in our example, the heat exchangers used in Scenario (1) and (3) are changed to water cooled heat exchangers, and hence, the seal support system will require water. Kerosene is selected for the Plan 32 injection fluid into the seal chamber for Scenario (2) and the injection fluid value is increased. Additionally, the value of the pumped fluid is increased. As this pump is considered critical, a cost of $5000 per failure event is selected to represent the impact to production in the event of a seal or system failure.
Modifying the LCC Inputs
Cooling water for heat exchangers
Kerosene value for Plan 32 injection
Pumped product value
Cost of lost production per failure event
Modifying the LCC Inputs
The pumping conditions can be added and the expected Mean Time Between Failure (MTBF) included.
A reduced MTBF for Scenario (1) is selected as it is expected that the performance of the heat exchanger will deteriorate over time due to the large heat load placed on it.
The MTBF for the heat exchanger is also modified to match that of the seal assuming the cooling coils would require cleaning on a regular basis.
Modifying the LCC Inputs
Pumping temperature
Reduced MTBF for scenario 1
Modifying the LCC Inputs
The purchase cost for the seal support systems are added.
▪ Scenario (1) requires a heat exchanger, stand and interconnecting piping.
▪ A closed loop barrier fluid circulating skid is selected for Scenario (3) with a significant initial investment cost of $50,000.
Modifying the LCC Inputs
Plan 23 heat exchanger and accessories
Plan 54 circulator skid & accessories
Plan 32 piping and instrumentation
The LCC Calculated Outputs
Detailed breakdown of consumables required for the seal support system and value of product leakage
Breakdown of costs associated to maintain the seal and support system together with lost production costs
Costs associated with direct power consumption and parasitic energy losses
The results produced by the LCC calculation tool give a detailed breakdown of the annual operating costs including the costs of parasitic losses.
The LCC Calculated Outputs
A summary is provided of the initial one-time cost (investment costs) as it is commonly used determining factor in the selection of a particular sealing solution.
In this example, there is a significant difference in the one-time cost between the sealing solutions examined. That difference is considered together with the operating costs over the projected life expectancy of a particular pumping asset, the resulting total estimated life cycle cost may provide a different outcome.
Additionally, a summary of the energy requirements of each scenario is provided together with the carbon footprint of each solution.
The LCC Calculated Outputs
In summary, when faced with the decision of evaluating alternative sealing solutions, the LCC calculation tool provides decision support that is:
Insightful
Comprehensive
Customizable
Specific The LCC calculation tool is available from the Fluid Sealing Association’s website: www.fluidsealing.com
