Perspectives: Energy Saver

Pump Out Energy Loss

Review the total pumping system to lower electricity bills significantly

By Ven V. Venkatesan, Energy Columnist

Running the pumps can account for more than 20% of the total electricity consumed in a plant. However, it’s not simply the pump and its drive that consumes all the energy, but the pumping system as a whole.

Pumping system efficiency is defined as the ratio of the actual work delivered by the pump in moving the fluid to the energy supplied to the motor drive. Only the required head and flow rates are considered in calculating delivered energy and system efficiency. Unnecessary head losses are deducted from the pump head, and unnecessary bypass or recirculation flow is deducted from the pump flow rate. Efficiency tests help engineers identify inefficient systems, determine energy-efficiency improvement measures, and estimate potential energy savings.

In a typical pumping system energy use is broken down as follows: piping pressure drop — 29%; throttling process — 25%; pump operation — 20%; actual delivered energy — 18%; and motor operation — 8%. From the breakdown, only 18% of the supplied energy goes for valuable work, making it the pumping system efficiency. The remaining 82% is wasted energy and available for more efficient operation. Often, wasted energy leads to high system maintenance. The motor drive that consumes 100% energy accounts for only 8% of the energy input. Yet, many utility incentives target energy-efficient motor replacement as the main means of energy reduction. In some cases, the old pump indeed may be the reason for excessive energy consumption. However, more efficient use of wasted energy can be identified only by comparing an optimum pumping system with minimum hydraulic pipe losses combined with the properly sized pump and motor and suitable controller to the actual pumping system. Hence, it’s better to look at the entire pump operation rather than looking at only the motor or pump’s efficiency.

A systematic approach for evaluating pumping systems begins with the following actions:  

1.    Survey all the pumps in your plant by setting priority groups such as pumps <100 hp, 50–99 hp, 20–49 hp and <20 hp.  
2.    Look for symptoms associated with inefficient energy consumption, such as throttle-valve control for the system, a bypass or recirculation line normally open, continuous pump operation to support a batch process, constant number of parallel pumps supporting a process with changing demands, cavitation noise or damage in the system, high or frequent system maintenance, and systems that have undergone change in function.
3.    Identify and list the misapplied, oversized or throttled pumps, or those that have bypass lines.
4.    If the manufacturer’s pump curves are available, verify those pumps’ operating points and if they are well below their normal efficiency.
5.    Conduct efficiency tests on all other pumps, with the help of portable clamp-on flow meters and power meters.
6.    Evaluate the potential reasons for efficiency loss and the remedial measures to restore the system to its original efficiency level.
7.    Estimate energy savings from restoring the system to its original efficiency levels.
8.    Estimate the cost for efficiency restoration and determine the cost effectiveness of each improvement and prioritize the improvement actions.
9.    Implement the prioritized actions.

Significant savings could result from improving the total pumping system. More-efficient operation could be as simple as eliminating unnecessary pumping or improving the control system to switch off a pump instead of recycling the discharge flow. For example, we identified unnecessary pumping between storage chests in the stock preparation section of a pulp and paper mill that later was eliminated by simple piping modifications.

Whenever a bypass (recirculating) flow control system from a pump discharge is continuously open, there’s potential to save energy. Though variable speed controls could save energy use, it may be possible to install a smaller pump and efficient control system for better optimization. In a published case study, a plant engineer looked at the total system when an old, frequently failing, constant-speed booster pump was due for replacement. The pump was always running and recirculating water through a bypass valve when the flow was low or there was no demand. Instead of replacing the pump, the engineer installed a new booster pump skid that had the combination of low-speed operation, no-flow shutdown and soft fill startup features. The booster pump skid optimized the discharge head and adjusted its speed based on system demand. When no flow is required, the pump could switch into “sleep mode” instead of pumping water through a recirculation valve. The net benefit was a staggering 65% reduction in annual energy consumed by the old booster pump.  


ven-head-shot.jpgVEN V. VENKATESAN is Chemical Processing's Energy Columnist. You can e-mail him at vvenkatesan@putman.net

More from this perspective...

Title

Use a portfolio approach to energy management

A business plan for industrial energy management is remarkably similar to financial planning, says Christopher Russell in his Energy Saver column.

03/01/2007

Use a multifaceted approach to manage your energy costs

One or two tools alone won’t allow you to maximize results, but this list of six common tools will help, according the Christopher Russell in this month's Energy Saver column.

02/12/2007

Understand Energy Management Basics

Five key activities can help reduce energy use.

06/20/2012

Turn Waste Energy Into Cash

Make the Energy Independence and Security Act pay off for you.

02/10/2010

Train Your Project Manager on Energy Efficiency

Treating energy saving measures as project add-ons can help.

09/07/2010

Train Your Plant Manager on Energy Efficiency

Present your energy program in a way the plant manager can quickly comprehend.

10/20/2010

Train Your Operators on Energy Efficiency

Provide them with the right information and listen to their ideas.

08/09/2010

Team Up to Save Energy

Collaborating with local utilities can further reduce energy costs.

09/18/2013

Take the right first step to manage your energy costs

Conducting an energy assessment provides a business plan for improvements and is the first step to managing energy costs, according to Chemical Processing's energy columnist Christopher Russell.

12/18/2006

Take a Fresh Look at Your Process Heaters -- Part 2

Three simple steps can help reduce stack temperature.

01/06/2011

Take a Fresh Look at Your Process Heaters

A simple four-step program can lead to significant savings.

11/30/2010

Tackle organizational obstacles

For energy cost control, aptitude plus operational style equals results, advises Contributing Editor Christopher Russell, in this month's Energy Saver column.

08/28/2007

Survey results reveal cost reduction strategies

Learn what large companies do to manage their energy costs in this month's Energy Saver column by Contributing Editor Christopher Russell.

08/20/2007

Some training courses are worth the price

Learn to use energy tools to make your plant more efficient

06/02/2008

Simplify Your Energy Message

Money loss calculators can spur better operator response to wasted energy.

08/04/2009

Say farewell to the old energy paradigm

Controlling costs in today’s market requires a different approach, says Christopher Russell, contributing editor, in this month's Energy Saver column.

10/01/2007

Save Energy in Water Systems, Part II

Recover cold cash from cooling water systems.

11/16/2011

Save Energy In Water Systems, Part I

Plants often miss opportunities to more fully use hot water.

10/13/2011

Save Cold Cash

Here are a few tips to keep your winter energy bills under control.

10/08/2009

Respond Right to Reduced Rates

Maintaining energy efficiency helps keep operating costs in check.

12/08/2009