Centralized Compressor Control Saves Energy at Ball Corporation
Do you know how much energy your air compressors are wasting? Many plant operators don’t, until they take a close look at their energy consumption and how their air compressors are being controlled. In fact, the U.S. Department of Energy suggests that air compressor power usage represents some 10% of all the energy consumed by industrial plants, and much of this energy is wasted.
The problem is that many compressors are controlled locally, either by mechanical valves and pressure switches or by electrical controls at the compressor. With no means of central system monitoring, it is not unusual to have multiple compressors running at partial load. In addition to using energy inefficiently, this situation results in unnecessary component wear and compressors fighting each other in an attempt to maintain pressure and airflow at different levels. The waste and extra cost as a result of operating compressors in this way can be greatly reduced or eliminated by installing a central control unit to manage the compressors.
How does a particular company know what inefficiencies exist in its own air supply system? The first step is typically to perform an energy audit. Such a study was made at the Ball Corporation aluminum container plant in Springdale, Arkansas. The study revealed that each of the plant’s five air compressors was in continuous operation (Figure 1), with the load fluctuating significantly from time to time on several of the compressors. In order to compensate for operational inefficiency and ensure that the minimum air requirements of the plant were met at all times, pressure set points were increased beyond the optimal values. Taken together, it was estimated that the Ball plant was wasting more than 20% of the energy it was using.
Centralized Compressor Control is Key to Energy Savings
The solution was to install a central sequencing controller to operate all of the plant’s compressors. A sequencer activates compressors according to a predetermined order as the controller works to achieve a target system pressure. At most, one compressor is allowed to run at partial output, while others are configured to run either at full load or are turned off. The result is a marked reduction in energy usage. For example, when a PL1000 target-pressure sequencing controller manufactured by Pneu-Logic Corp. of Portland, Oregon (Figure 2) was installed at the Ball plant, rather than all five compressors running virtually all of the time, the compressed air needs of the plant were met by just three compressors: two running at full load and a third compressor (a new variable-speed trim compressor) running at partial load as required. Figure 3 shows the result of an energy audit made after the plant upgrade.
With the new controls, the pressure at the plant is more stable – approximately +/- 3 psi – compared to the old scheme, where the pressure was fluctuating +/- 12 psi. This allowed Ball to reduce the average discharge pressure by 10 psi, further reducing the system’s energy usage.
All told, installing the controller resulted in more than a 20% reduction in the total horsepower required by the compressor network, and a post-upgrade audit revealed that the system pressure could be reduced by an additional 6 psi due to the precise control implemented by the sequencer. With this level of savings, payback on the control system investment was achieved very quickly.
Airgonomics Balances Air Supply with Demand
Though effective in implementing basic control functions, a limitation of some sequencers is the lack of flexibility in implementing different control strategies. In designing their controllers, Pneu-Logic Corp. comprehends the need to be flexible in balancing air supply with demand by coining the term Airgonomics, which refers to the way that the company’s controllers intelligently manage compressor resources to meet air demand. Airgonomics suggests that it’s not always the right thing to do to run the most efficient compressor next. If it were, then that compressor would wear out first. The system needs to take preventive maintenance factors into account, as well as other environmental factors that can affect the choice of compressor units.
By using a flexible Pneu-Logic control unit described above, Ball Corporation plant operators can be assured that another industry “best practice” is in place, contributing to the goal of running a more energy efficient and sustainable plant. Managers of other facilities can learn from this example: With active controls enabling the optimization of energy consumption, the production of compressed air can be viewed as having a variable cost like any resource used in the manufacturing process, and it can be controlled to maximize productivity and minimize waste.