Thanks to steady, targeted growth in the first decade of the new century, the number of global biofuel production plants stands at roughly 1,000 – with 600 dedicated to the production of ethanol and another 400 used to produce biodiesel – with some additional growth expected through the remainder of this decade, notably in the United States and Brazil.[1] These plants will be servicing a worldwide biofuel industry that is expected to produce 42.3 billion gallons (160 billion liters) of ethanol and 10.8 billion gallons (41 billion liters) of biodiesel by the year 2019.[2]
A key component in keeping these biofuel-production plants operating smoothly are pumps, more specifically, centrifugal pumps, with many plants employing many of them at a time for operations as varied as raw-product transfer, actual fuel production, and loading and transloading to trucks and railcars. In order to keep the pumps in tip-top operating condition and the facility functioning as expected, they need to be properly maintained. This article will focus on ways that centrifugal pump operation in biofuel plants can be maximized through proper maintenance schedules and procedures.
Why centrifugal?
Since the first models were invented, centrifugal pumps have moved liquids through the use of centrifugal force. This makes them kinetic machines in which pumping energy is continuously imparted to the pumped fluid by means of a rotating impeller, propeller or rotor. It also makes them ideal for biofuel-production operations. Currently, the three most common styles of centrifugal pumps are:
- ANSI: These pumps meet centrifugal-pump manufacturing criteria established by the American National Standards Institute (ANSI) in 1977. With that standard in mind, ANSI centrifugal pumps are engineered for operational flexibility and durability. ANSI pumps also can be end-suction or self-priming, in-line, etc., styles.
- End-suction: Ideal for thin liquids and the top choice for most water-pumping applications.
- Self-priming: This type of centrifugal pump has the ability to lift fluid, which gives it an advantage when the source is below the centerline of the pump.
No matter the operational atmosphere where these types of pumps are being used, a routine maintenance program will extend the life of the pump since well-maintained equipment lasts longer and requires fewer and less-expensive repairs. Many biofuel plant operators are performing a life-cycle cost (LCC) analysis that factors in the lifetime costs of maintenance, along with purchase, installation, energy usage, operation, downtime, environmental and other costs when choosing the proper pump technology for the operation. According to the Hydraulic Institute, while energy, at 40 percent, might represent the highest expected pumping-system-related expense in an LCC analysis, the second-most costly is often maintenance, at 25 percent.[3]
Maintaining an edge
When the pump is purchased, the manufacturer will advise the plant operator about the frequency and extent of routine maintenance, but it is the operator who has the final say about how his facility’s maintenance routine will function, i.e. whether it consists of less frequent but more major attention, or more frequent but simpler servicing. The maintenance routine should also determine what steps should be followed when a breakdown occurs, while a post-repair assessment should identify areas where proactive maintenance might have prevented the breakdown.
The facility operator also should keep a detailed record of any preventive maintenance that was performed and repairs that were needed for each pump. This information is kept in order to create an easily accessible record that can help diagnose problems and eliminate, or minimize, any future equipment downtime.
Moving into the nuts and bolts of centrifugal-pump maintenance, routine preventive and protective maintenance practices should include, at a minimum, the monitoring of:[4]
- Bearing and lubricant condition. Monitor bearing temperatures, lubricant level and vibration. The lubricant should be clear with no signs of frothing, while changes in bearing temperature might indicate imminent failure.
- Shaft seal condition. The mechanical seals should show no signs of visible leakage. Any packing should leak at a rate of no more than 40-60 drops/minute.
- Overall pump vibration. Imminent bearing failure can be preceded by a change in bearing vibration. Unwanted vibration also can occur due to a change in pump alignment, the presence of cavitation or resonances between the pump, its foundation or the valving located in the suction and/or discharge lines.
- Differential pressure. The difference between the readings at the discharge and the suction of the pump will provide the total developed head pressure of the pump. A gradual decrease in the developed head pressure of the pump can indicate that the impeller clearance has widened, which requires adjustments to restore the pump’s intended design performance: impeller clearance adjustment for pumps with semi-open impeller(s) or replacement of the wear ring(s) for pumps with closed impeller(s).
