Pumps & Systems, July 2013
Large pump packages allow for a high hydrodynamic power output, a high overall efficiency and reasonable costs. Several different factors have affected the evolution of large pump packaging for industrial plants. Some of these include:
- Pump capacity and power density increases
- Tighter health, safety and environmental (HSE) standards, expectations and regulations
- Higher expected reliability and availability
- More compact package design
- High expectations for easy access and ease of operation and maintenance
Large modern plants and new generations of small-scale units present challenges to pump packaging. There is renewed interest in small scale plants in different parts of the world, particularly in some developing countries. The packaging of a pump for a small-scale plant should help minimize the equipment/item count (and process steps) to optimize capital costs and the footprint, while obtaining the highest possible efficiency and reliability.
On the other hand, some new, large plants present different challenges. In some industrial sectors, the throughput per train has multiplied by a factor of about 5 to 10, and the overall efficiencies of pump packages have increased. At the same time, the duration of construction and commissioning of plants has decreased, which means more modular works and prefabrication for large and complex pump packages. Deep integration and the modular design are keys for success in modern pump packaging.
The large pump skid market is unlike other markets, and the large pump market is dynamic. Packaged systems should include certain components, equipment and capabilities to operate successfully. The pumps, variable speed drives, adherence to specific standards and an appropriate oil lubrication system should all be carefully considered when selecting or designing a packaged system.
An example of an engine-driven packaged pump system
Industrial pumps range from small pumps (below 10 kilowatts at an installed cost of nearly $100 to $700 per kilowatt) to pumps rated above 5 megawatts at a cost of $25 to $300 per kilowatt. A two-bearing design is preferred in single-shaft pumps. Three-bearing solutions could cause problems—such as misalignment because of the center bearing—but they could be options for very large single-shaft pumps (rarely used except for some special applications).
For axial pumps, some problems can occur if the number of blades changes greatly between stages. Some specifications have allowed for the slight rubbing of rotating parts. This is not a popular option for operators. Excessive rubbing is always unacceptable.
More flexibility is required for modern plants. Operational and production flexibilities, variation in production volume and flexibility in production grade/quality are important. In many applications, the tendency is for industrial units to increase part-load operation capabilities (a wider part-load range with the performance and operation quality comparable to the full-load service).
An example of a vertical pump skid that contains two large vertical pumps
VSD, electric-motor-driven centrifugal pumps are ideal choices for many pump applications. High efficiency is one important issue that encourages the use of pumps with VSDs. A pump’s initial cost is about 20 percent of its total life-cycle cost. The operational and maintenance costs are approximately 19 percent of the total life-cycle cost. The cost of power to run the pumps is about 61 percent of the total life-cycle cost, which indicates the critical role of the pump efficiency.
While pump system energy efficiency has made significant progress during the past 40 years, this can mainly be attributed to VSD systems and a better integration of pumps in modern industrial plants. VSDs and proper integration can account for a significant part of the overall efficiency improvement of pump packages during the last four decades.
Standards and Requirements
Standards for pumps and pump auxiliaries (for example, API 610, ANSI, and others) are the minimum requirements for specified applications in each code. However, some requirements that could be beneficial to an application are only listed as optional in pump-related codes. In many instances, simply following all the stated requirements (mandatory and optional requirements) for the pump packaging is sufficient. However, some applications would benefit from packaged pump suppliers looking beyond the pump codes to achieve a higher level of performance and reliability. End users should follow these guidelines regarding pump codes:
- Codes are usually updated every 5 to 10 years. Recent technologies, innovative designs, latest observations or new experiences need several years to be accepted by a code task force teams and incorporated into codes.
- Groups working on codes and standards should include representatives from different groups and vendors and team members with different backgrounds and goals. The main focus of pump codes are not always the best performance and reliability for the operators, but usually the final or agreed upon specification is an optimized (compromised) requirement.