Efficiency of Pumps
Pumps are everywhere in modern industry. For water supply systems, wastewater treatment facilities, factories, refineries or power plants, we rely on pumps to drive processes or simply to move water to where we need it. Of course, all this activity requires energy – lots of energy.
Improving Energy Efficiency of Pumping Systems – A systems approach
According to a study prepared by a major European industrial research institute, approximately 20% of the energy used by industry is consumed by pumps and related equipment. Closer to home, the US Department of Energy has estimated that the total energy consumption of industrial pumps in that country is 142,000 GWh/year – enough electricity to power over 13 million homes! Studies also indicate that energy costs are the largest single factor in the total cost of ownership of pumps in industrial settings. With the steady increase in energy prices worldwide (to say nothing of the pressure to reduce greenhouse gases) there is more and more need for the designers and managers of industrial facilities to pay close attention to the energy efficiency of the equipment they operate. © KSB Aktiengesellschaft
KSB, one of the world’s largest manufacturers of centrifugal pumps, is tackling the energy efficiency issue head-on with a multi-faceted strategy that addresses all aspects of energy use in pumping systems. The “Fluid Future®” initiative is aimed at helping pump users optimize the performance and minimize the full life cycle cost of pumps and the systems they help drive.
Taking a systems view
The starting point is a comprehensive overview of the operating conditions under which each pump will operate. This includes head, flow rates, temperatures, the type of fluid being pumped and the presence of solids, abrasive materials etc. It is also important to look at the full plant environment and the economic drivers behind the development.
Selecting the right equipment
Once the full operating envelope for each pump has been determined, it’s time to select the best piece of equipment for the job. This isn’t always a simple task, given the enormous variety of pumps available on the market. And, once an appropriate type of pump has been selected, it’s equally important to specify the optimal size and configuration. This might involve the selection of impeller types, seals, special corrosion or wear-resistant materials and so on. KSB’s EasySelect® selection and configuration software can be a valuable tool for narrowing the search. Naturally the help of a skilled application engineer is also important for confirming and refining the choice.
Attention to detail: a key to improved energy efficiency
It’s well known that each pump has a ‘best efficiency point’ (BEP) or sweet-spot – a combination of head and flow rate where it will deliver its best performance in terms of both energy efficiency and service life. A key to getting the best overall system performance is to make sure that each pump in the system is operating as close as possible to its BEP. This isn’t always easy. Flow and pressure requirements can vary significantly, especially in water and wastewater systems that need to respond to changes in demand as well as events such as stormwater surges. In many systems, friction losses can gradually increase due to corrosion or sediment build-up in pipes, which means that the pressure needed to push fluid through the system increases over the life of the pump. © KSB Aktiengesellschaft
There are several possible strategies for dealing with these challenges. For many of KSB’s more popular pump families, a wide range of sizes and capacities are available, which means that it is possible to select a machine that has a BEP close to the required duty point. Impeller trimming can be used to further refine the fit. This is a process of reducing the diameter of a standard impeller to slightly reduce the output of the pump. Done properly, this shifts the BEP so that the optimum performance of the pump precisely matches the requirements of the application. IN KSB’s experience, optimizing pump performance through impeller trimming will improve overall energy efficiency by 10% on average.
Where flow requirements change significantly, one of the best approaches is to have the load shared by a number or smaller pumps that can be operated independently. Here, the number of pumps running at any time will be set to match the overall flow requirements, with each individual pump operating near its BEP. Fine-tuning can be done by having one of two pumps equipped with variable frequency drives (VFDs). VFDs are control devices that enable an operator to adjust the speed at which a pump runs. This enables the operator to adjust the output of the pump, while still having it run at near-optimal efficiency.
A further step in maximizing energy efficiency involves the use of ultra-high-efficiency motors. These tend to be more expensive than conventional electric motors, but over the lifetime of the pump set – which can easily exceed 20 years – the extra cost is usually recouped.
In Europe, a new directive – called ErP for ‘Energy-related Products’ – have established a set of increasingly stringent targets for energy efficiency in certain classes of industrial equipment. Products that do not meet the appropriate efficiency standards for their class will be banned for sale in Europe. To meet these demanding targets, KSB has undertaken a programme to improve the efficiency of its most popular pump families through:
- Careful re-design of pump hydraulic elements, carried out through a combination of Computerized Fluid-Dynamic (CFD) analysis and extensive laboratory testing;
- An increased number of size options, which makes it easier for customers to find a pump with characteristics close to the application duty point; and
- The adoption of ultra-high-efficiency motors and the use of variable speed drives, to further reduce electricity demand.
KSB has adopted a proactive approach here to ensure that their customers have access to products that meet the emerging standards. And, while customers outside of Europe may not be directly subject to these regulations, they will benefit from improvements to energy efficiency and the resulting reduction in operating costs.
Energy Efficiency in Action
At KSB Canada, our application engineers and specialists use the Fluid Future principles to pump owners reduce their energy bills and total cost of ownership. Here are some examples of how this is being achieved.
Pump modifications to reach the ‘sweet spot’
When a pulp producer in western Canada downsized their mill in response to changed market conditions, they found that their boiler feed pumps were oversized for the new operating requirements. Instead of replacing the pumps, KSB and its partner, Inproheat, recommended replacing the existing 50 year old pumps’ internal hydraulic components with new impellers and diffusers so that the pumps’ optimal operating point matched the new requirements. This resulted in a 23% improvement in energy efficiency compared to running the pumps in their original configuration and reducing flows by valves or orifice plates.
Sometimes more pumps are the best answer…
A large municipality required a flexible pumping solution for a wastewater treatment plant. In order to handle highly-variable flow rates, a multi-pump configuration was proposed. The majority of pumps were to operate at fixed speed, close to their best efficiency point or BEP, while the two pumps would be equipped with VFDs. The operator could meet a wide range of flow conditions by varying the number of fixed-speed pumps running at any time, then fine-tuning the output of the two variable speed pumps. KSB Pumps worked with the client’s engineer to optimize the number and specifications for the pumps. Making sure that each pump would operate close to its best efficiency point reduced the projected energy costs by a significant amount. Careful design of the complete configuration also reduced the capital cost of the facilities in which the pumps would be housed, thanks to optimization of the size of valves and pipe work.
…And sometime fewer can do the job better!
A company in northern Alberta was launching a pilot project using an innovative process to extract bitumen from oilsands deposits. The project aimed to produce 10,000 barrels of oil per day with no net water use.
The customer initially requested two high-pressure boiler feed-water pumps (BFWP), plus two booster pumps that would be configured to feed BFWPs. By helping our customer select a type of pump that didn’t require a booster, we helped them save about 15% of the overall capital cost of the pumping system. Reducing power consumption and maintenance will ensure further savings over the long run.