Tips for reducing energy use16 May 2023

Sulzer energy

Within the water treatment industry, aeration processes consume the most energy. However, costs for electricity are continuing to rise. Reviewing current processes and taking advantage of some modern technology are just two ways to potentially reduce running costs, according to Edward Paro, global product manager for compressors and aeration at Sulzer

Any project involving capital expenditure (CAPEX) needs to include a calculation for the return on investment (ROI). Now, with rapidly rising energy costs, the ROI for any energy-saving project that reduces power consumption will be significantly shorter than in the past, giving it a much better chance of approval. The best way to support any request for investment is by delivering solid figures for savings that show how quickly the finance can be recovered. One way to achieve this is to do an audit. The amount of electricity consumed is usually easy to determine, but what do you get for it? It is advisable to take care to measure parameters such as for example the output of the blowers with instruments that are up to the task. Information on blower displays or permanently installed legacy instruments may give the wrong impression about the efficiency of the operation. It is better to verify the actual flow with a stand-alone instrument. This is just one tip to cut bills; below are more.

First, as any improvement project is going to require an initial investment, the key is to recover this cost as quickly as possible. It is important to understand exactly how much energy costs are rising and how this is affecting the business’ performance. For example, since aeration is the single largest energy-consuming process in a water treatment plant, this is where the greatest single improvement can be achieved.

Fixing leaks and imbalances should be a top priority. For example, monitoring the back pressure over time will help understand how clogging of diffusers affects the efficiency. However, exchanging components such as the diffuser system or the mechanical aerators is usually a major undertaking, with a potential impact on process operation. That type of refurbishment is often best done in conjunction with other major upgrades or when the aeration system is reaching the end of its life.

Second, consider mixing and matching old and new. While many operators will strive to do a full exchange of all legacy blowers in one, completing the refurbishment as a step-by-step process offers significant advantages. One good strategy is to install sufficient equipment to cover the base load air requirement for the process, ensuring the new machines run continuously, with the older, less efficient equipment only being called on during periods of high flow.

New technologies such as blowers with magnetic bearings will have no mechanical wear and thus do not need to be cycled out of duty to even out wear. This in turn means that the legacy machines will be standing still and, even if they wear, the lower operating hours will extend their economic life, decreasing maintenance and service charges. This strategy ensures the savings in energy consumption are maximised and the time to recover the investment is kept to a minimum.

Third, reduce project times. The less time required to complete the project, the quicker the savings will be realised. In many cases, a containerised blower can be installed without additional permits and with a bare minimum of civils construction. They can be used as a permanent solution to replace existing equipment, or as a temporary solution while the original equipment is replaced with more energy efficient machinery. They can also be used in locations that are expected to have a limited operational life and relocated to another site later, maximising the efficiency benefits for both sites.

Fourth, use a step-by-step process. Even if the target is to replace all blowers eventually, it may be wise to divide the project into smaller steps. This will help to successfully secure the necessary budgets, which may be gathered from operational expenditures (OPEX) as well as CAPEX. With such a significant potential saving in running costs, the controller of the OPEX budget may realise the benefits that can be achieved and release funds to get the project started. Each refurbishment project will include some need to change electrical installations, re-route or update controls as well as adapt the pipework to fit the new machines. Such preparations can be broken out and executed while the older blowers remain in place. The blowers themselves can be ordered to be delivered over a period of years in order to fit under CAPEX ceilings.

Fifth, look to downsize. Often, due to many treatment plants being over-sized for the flow that is received, the equipment that is installed will also be over-specified. This is quite normal, as designers expect the surrounding population to grow during the lifetime of the equipment on site. However, advances in wastewater treatment process efficiency mean less air is needed, whereas the focus on minimising water use has meant that increases in flow have not materialised or inflows may have decreased.

Sixth, contrarily, look to upsize, in some applications. Some installations may consist of numerous smaller blowers that need to work in unison to match aeration process demands. In this case, replacing two units with a single, more efficient model will achieve a reduction in operational costs while minimising the capital expenditure both on machinery and installation. The bigger blower may be too big for the night-time low flow regime, however. For this, a limited number of the legacy, smaller blowers could be retained. The lower efficiency of the legacy blower will not have a large impact because the overall energy consumption for the lower flow, and hence power, is small during the hours in question.

Seventh, try to reuse old pipework. Modern high-speed blowers are usually smaller than their legacy counterparts and can more often than not be connected to the existing aeration pipework, which can minimise project costs in terms of civils and materials as well as the overall time required to complete the project. By working with an experienced design and manufacturing team, it is possible to make the best possible use of the existing infrastructure without compromising the performance of the new equipment.

Eighth, consider controls carefully. As part of the update project, a review of the control infrastructure for air production and how it can be optimised to make the most of the new equipment and reduce operating costs for the aeration process. Consider replacing legacy controls by one master controller for the complete set of blowers, including the legacy blowers left in place.

In summary, the savings that can be made by improving the efficiency of plant such as blowers will enable initial investments to be recovered even more quickly than before.

While this text has outlined a number of strategies, each treatment plant is different, however, and needs to be evaluated to find the true potential for saving energy. A good place to start is to contact companies with expertise in the field to do a thorough survey of the most promising candidates.

Edward Paro

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