Energy Efficiency of Pumping Systems in Pulp and Paper

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Energy Efficiency of Pumping Systems in Pulp and Paper

October 17, 2016 - 10:21
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Industrial manufacturing faces an increasingly competitive environment. Companies are looking for opportunities to reduce production costs without impacting on their productivity or the quality of the end product. One of the most effective methods is to concentrate on energy efficiency. This will also have additional benefits in terms of improving green credentials.

Saku Vanhala, Product Portfolio Manager, Pumps and Agitators, at Sulzer, examines how the energy efficiency of pumping systems can be improved, especially in regard to the pulp and paper industry.

Worldwide industrial energy consumption is expected to increase by 42% between 2007 and 2035, or an average of 1.3% per year. Pumping systems account for more than 20% of the world’s electrical energy demand, and in certain industrial plant operations they can be responsible for between 25% and 90% of the energy usage. The pulp and paper industry is certainly over the midway point of this spectrum.

Throughout any manufacturing process, energy is lost due to equipment inefficiency as well as mechanical and process limitations. Optimizing the efficiency of pumping systems can result in significant energy and cost savings as well as reduced carbon dioxide emissions. Understanding how energy is used and wasted can help plants pinpoint areas of energy intensity and ways to improve efficiency.

Pumping systems consist of the pump itself, a motor, piping, valves and instrumentation. The energy and materials used by a system depend on the design of the pump, the design of the installation, the process conditions and the way in which the system is operated. Furthermore, all these must be carefully matched to each other as well as to the application throughout their entire lifetime to ensure the lowest energy and maintenance costs.

The initial purchase price is usually a small part of the whole life cycle cost for industrial pumps. While operating requirements may sometimes override energy cost considerations, an optimum solution is still possible. A greater understanding of all the components that make up the total cost of ownership will provide an opportunity to dramatically reduce energy, operational, and maintenance costs.

 

Figure 1: Life cycle costs of a pumping system

 

It is self-explanatory that the reduction of energy consumption is a key component to controlling costs in pumping systems. Using the right pump technology, properly sized for a specific application, is an important step towards reducing pump energy consumption. This can be achieved by focusing on the pump efficiency and minimizing all possible losses in the system.

Direct Savings by Optimization of the Pumping System

Opportunities for energy savings in pump operations are often overlooked because pump inefficiency is not readily apparent. A pump usually sits in a basement and as long as it runs, it generally does not get much attention. There are many ways to make substantial savings during the pump lifetime, all the way from the design phase through procurement, operation, and maintenance. Direct savings can be made with the right selections and decisions in your pumping systems including pump, drive method, pumping system lay-out and maintenance.

Premium Efficiency through Optimized Pump Selection

The most significant savings in the energy consumption of a pumping system can be achieved by selecting the most appropriate pump technology for an application with premium efficiency. This selection process starts with gaining a complete understanding of the application, fluid characteristics and flow demands. This information is then brought together with a comprehensive knowledge of pumping technologies to deliver the most appropriate pump that will provide optimum performance and energy saving results.

Matching the most appropriate pump construction with the optimum impeller design will result in the most cost effective solution, both in terms of initial capital investment and long term operating costs.

The correct sizing of the pump represents the next most significant economic opportunity to reduce energy consumption. Oversizing often occurs in the design phase by the customer, because it is quite common to add multiple safety factors to the required head and flow values.  As a consequence, an over-sized pump is selected and therefore the pump does not run within its best efficiency area during normal production, resulting in a considerable waste of energy.

It is important to point out that the rotational speed of the pump directly affects the pump size and its efficiency. With clean liquids it is safe to select higher rotational speeds and maximize the efficiency and energy savings. Fortunately, nowadays 3,000 rpm pumps are being accepted for various processes, bringing direct savings to the end users.

The table below shows a comparison of various process pumps suitable for a particular process water application. The differences in design between the three pumps have a significant effect on both the initial purchase price and the annual energy consumption. Making the correct decision in pump selection can have a huge impact on annual running costs, considering that there are more than one hundred pumps in a paper mill.

 

Figure 2: A comparison of costs for different pump selections

Replacing a pump with a new, high efficiency design reduces the energy consumption normally by between 3% and 20%, but in some cases there can be as much as a 50% reduction

The best pump selections can be achieved by working closely with Sulzer’s pump experts. It is important to get information on the actual values of the desired running point and also on possible future expansion demands. This information enables the Sulzer engineers to select the optimal pump type, size, speed, power requirements, type of drive, as well as the seal and auxiliary equipment.

Sulzer operates a pump optimization program that also enables the clients to see the saving potential of each pump unit and provides a range of options that can be delivered in order to achieve the projected savings.

Improving Performance with Variable Speed Drives (VSD)

The best efficiency and further energy savings can be achieved by driving the pump with a variable speed drive (VSD) and a maximum diameter impeller. This allows the rotational speed of the pump to be adjusted to achieve the desired head and flow for the process application. The efficiency improvement compared to a constant speed driven pump can be up to 10%.

A VSD can be added also to existing pumps and once installed it can accommodate changing system demands, including potential future expansion plans without changing the pump.

In addition to energy savings, this method also results in improved process control, improved system reliability, reduced maintenance costs due to reduced wearing, and soft starter capability. This is why VSD driven pumps are becoming more and more common in the process industry.

Eliminating Losses Gives Maximum Savings

The pumping system pipework lay-out and flow control devices that surround the pump have a detrimental effect on the total pumping efficiency. Factors such as pipe size (diameter), overall pipe length, pipe surface roughness, as well as control valves will influence the system pressure drop and resulting energy consumption for the system.

The use of control valves should be avoided wherever possible. These valves may jeopardize the savings achieved by premium efficiency pumps. Instead, variable speed drives or on-off regulated systems do not cause losses and therefore they save energy. The extensive use of throttling valves or bypass loops is often an indication of an unbalanced process or an over-sized pump.

In situations where an over-sized pump has been identified, replacing the pump with a more suitable design size brings a great potential for savings. In some cases significant savings can also be achieved by modifying the existing pump with a different kind of impeller or adding a VSD.

Figure 3: Potential energy savings that can be achieved by removing throttling valves and using a smaller pump

Proper pump selection and engineering of the piping system will accumulate big savings in energy and investment costs, but is also a key factor for successful process runnability.

 

 

Maintaining the Premium Efficiency

Having assessed and specified the most suitable pump for the process, the pump will run close to its best efficiency point. In such conditions the pump is working in an optimal way with minimal vibrations and losses.

In order to avoid unexpected problems and costs, it is good practice to monitor the pump performance and mechanical condition frequently. One of the best indicators to monitor is the power consumption as a function of the flow rate. This value will highlight any issues with worn hydraulic components or increased mechanical friction, which can cause a reduction in efficiency even up to 20% while still in effective operation.

Combining this preventive maintenance attitude with the use of original spare parts ensures the highest performance and continued reliability of the pumping system, whilst avoiding unexpected failures and maximizing productivity.

Sulzer has an experienced global service network to help its clients in all their pumping questions and needs. Sulzer offers full service availability for daily maintenance, pump optimization, and complete energy audits.

More Savings with Future Solutions

High energy prices have caused all production units worldwide to look for more energy efficient solutions for pumping processes. If a company leaves this opportunity unused, it may soon affect its financial performance, productivity and competitive position. It is Important to control the energy expenses by reducing power consumption without compromising the output performance.

Various directives and standards guide the process industry and thereby also Sulzer’s target setting in terms of efficiency. One important energy efficiency directive is set by the European Union (EU), which has created ErP (Energy-related Products) regulations. These regulations specify the minimum efficiency values for water pumps with the target of reducing energy consumption. Similar types of directives and regulations are being prepared all over the world.

Sulzer not only fulfills these requirements, but exceeds them, bringing maximum savings for its customers. A good example is the SNS process pump series that Sulzer launched in 2015. The SNS pump has set the standard for efficiency in its class.

 

Figure 4: SNS premium efficiency end-suction pump

 

Sulzer offers all industries the most efficient and reliable pumping solutions. Extensive research and development work at Sulzer has produced innovative solutions targeted at even better efficiencies and mechanical solutions.

In addition to the selection of extremely efficient pumps, more savings may be achieved by intelligent pumping process controlling and optimization tools in the future. Remote monitoring, controlling and optimization of pumps are already in use for specific processes. This technology will soon be used even more in industrial pumping processes.

Sulzer is renowned for state-of-the-art products, performance, reliability and efficient solutions, providing the highest customer value. For information on the efficient Sulzer pumping solutions for all pulp and paper applications, visit sulzer.com or contact your local representative.