Towards the energy-intelligent pump

Frankfurt, Germany – With pumps consuming an estimated 20-25 % of the electricity produced worldwide, and the process industry accounting for a quarter of that total, reducing energy consumption of pumps was not surprisingly a major theme at Achema 2012 in Frankfurt.

According to a briefing report by Achema organisers Dechema, most pump systems currently in operation are equipped with centrifugal pumps. The figure worldwide is estimated to be around 73% and can be as high as 85% to 90% in specific sectors such as the chemical industry.

Well engineered pumps and optimal configuration of the hydraulic system appear to offer the best route to maximum energy efficiency, said the report. Ongoing maintenance, it noted, can also reduce energy consumption, because wear and aging reduce the efficiency of all types of equipment.

A study by the FfE Research Center for Energy Economics indicates that the energy efficiency of poorly maintained pumps can decrease by as much as 15% .In practice, diaphragm pumps are often twice as efficient as centrifugal pumps. However, the efficiency levels which are theoretically possible with displacement pumps are not always achievable.

Friction losses, which are a particular problem in this regard, can be broken down as follows: gear unit (5 % to 40 %), plunger packing (1 % to 20 %), bearings (up to 3 % depending on the oil level), churning losses (up to 3 %) and the hydraulics (2 % to very high levels).

Possible solutions listed in the report include:
- Higher efficiency gear units (toothed gearing, belt transmissions)
- Improved bearing efficiency (no gaskets, lean lubrication, optimal viscosity)
- Lean lubrication with the lowest possible viscosity to minimise churning losses
- Selection of the shortest possible seals with small seal faces
- Effective pulsation management on displacement pumps reduces losses by more than 1 %. Under normal conditions, pulsating flow increases pressure losses. Continuous flow saves energy and reduces stress on all system components.

The European Ecological Design Directive (ErP) requires manufacturers to improve the energy efficiency of their equipment over the entire lifecycle and reduce the environmental impact. Pumps are no exception.

The motor regulation (EC640/2009) applies to nearly all motors rated between 0.75 kW and 375 kW as follows:
Stage 1: as of June 16th 2011 all motors must be IE2-compliant.
Stage 2: from January 1st 2015 all electric motors rated between 7.5 kW and 375 kW must either be IE3-compliant or IE2-compliant with a frequency converter.
Stage 3: from 2017 all electric motors rated between 0.75 kW and 375 kW must either be IE3-compliant or IE2-compliant with a frequency converter.

Minimum efficiency standards have been in effect for years in the US, where the proportion of high-efficiency motors (IE2) is much higher than in Europe.

The ErP Directive is based on the realisation that not using energy is the best solution from both the ecological and economic point of view. A study carried out by the German DENEFF energy-efficient business initiative indicates that energy savings by businesses and households could eliminate the need for electricity generation by ten nuclear power stations.

The standard principles of good pump design (working point close to the optimal pump operating point, hydraulically correct pipe dimensioning) and the technologies which are currently available to reduce energy consumption should be exploited to the fullest extent possible.

FfE Research Center for Energy Economics has provided some guideline figures for 2009. The investment costs are comprised of the cost of the frequency converter (€100 to €200/kW pump rated power) and installation costs of around €2000 per pump unit.

Impeller modification is another method which can be used to adapt centrifugal pumps to the specific application and reduce pump energy consumption. Reduction of pump and motor power ratings can cut energy consumption by between 10 % and 40 %. Modification can cost up to €1000 depending on impeller size.

Variable speed drives not only save energy and money. They also provide interactive capability. Pumps with sensors and microelectronics become actuators which can “intervene” and affect the process flow.

Communication-enabled pumps with parameterization features can ensure that a desired pressure level and volume flow are available in the reactor at a certain point in time or that exactly the right mixture of two substances is added at precisely the right moment.

Compared to mechanical control with butterfly valves, etc., flow rates can be controlled far more accurately and reaction times are shorter when variable speed drives are used.

E-pumps adjust the flow rate to match actual demand much faster and with greater precision in response to demand fluctuations. Variable speed pumps are more energy efficient, and they also help stabilize the process.

Overcoming obstacles

If that is the case, why then have users not taken advantage of all optimization options?

The Dechema report lists a number of possible explanations:

- Decisions are based on payback time: at many companies, the maximum payback period is two to three years. The payback period however is basically a risk management tool, but says nothing about ROI is the method to use for that purpose.

- Lack of a basic technical understanding: the people responsible for energy management cannot present the information in a way that managers without engineering expertise can understand.

- Spending constraints: approval is not given for any investment that is not absolutely necessary.

- Lack of human resources: opportunities to save energy are understood, but no one has time to take the appropriate action.

- Investment only when faults occur: reinvestment is often only considered when systems actually fail. In such situations, the new system must be available quickly and cost as little as possible. No thought is given to lifecycle costs.

- Failure to allocate costs: many companies only know what their overall energy consumption is. No consumption data is available for individual equipment. In many cases, personnel costs for maintaining old equipment is not allocated to the specific items.

- Without information on energy consumption and labour costs for the existing equipment, there is no way to identify inefficient equipment, and a financial evaluation of equipment optimisation is not possible.