System Assessments

During the summer season, vegetables tend to deteriorate quickly once harvested from the field—or during postharvest stage of the cold chain. In traditional cold chain systems, vegetables are put into a chilled cooler for preservation, a process that requires approximately 12 hours for the product to achieve proper temperature. In some instances, as much as 25 percent of food product in the chilled cooler will decay before arriving at a proper storage area. Fortunately, there is a process for improving the effectiveness of the postharvest stage—vacuum cooling.

Compressed air audits are valuable exercises on significant energy users in a plant.  Often done on main compressed air systems, these studies are also valuable on secondary systems, like dedicated low pressure circuits that feed production machinery.  An audit of such a system turned up some surprising results on a process that was initially thought to be very efficient.

Air-driven Venturi vacuum generators have long been a viable option for fast-response, localized, vacuum-powered systems. Through the last decade, they were considered convenient and flexible solutions with quick response time. However, they were not regarded as energy efficient, probably due to their use of compressed air. Extensive product development with this equipment — particularly the crucial system accessories — often makes the selection of the most energy-efficient items difficult for many localized operations.

The design of wastewater treatment plants is changing, and it has something to do with LEGO® bricks. More specifically, it has to do with how large and complex LEGO structures are built. If you follow the instructions carefully, you build module after module, eventually piecing them together to create a fully functional and cohesive unit.

A replacement strategy for air compressors and blowers integrated into a system-level approach towards energy efficiency can deliver significant energy savings and optimize equipment performance. At the Victor Valley Wastewater Reclamation Authority, a blower replacement project yielded annual energy savings of more than 928,000 kWh and $98,000 in energy costs, while improving the reliability of its secondary treatment process. In addition, the agency qualified for important incentives from its electric utility — significantly improving the project economics and resulting in a 2.94-year payback.

Aeration tanks use bubble diffusers to distribute oxygen within the wastewater. Fine bubble diffusers, or those that produce a large amount of very small air bubbles, first began to become popular in the 1980s, as they had a much higher efficiency than coarse bubble diffusers. Fine bubble diffusers generally feature a membrane that allows airflow to pass from the piping system on the floor of the tank through the body of the diffuser and the membrane, providing oxygen into the wastewater for treatment.

“What is the best type of oil to use in my vacuum pump?” is a common question for sure, and one that may often yield confusing and conflicting answers. The rule of thumb is that it is always best to follow OEM recommendations, but why do they recommend the lubricants that they do? For the purpose of this article, we will focus on some of the general industrial vacuum pump applications and their lubricant choices.

The overall wastewater treatment process is complex, and each step is integral to ensuring water is properly purified. Effluent ends up in the plants, containing substances that must be removed before the water can be properly cleaned and returned for use. The range of potential contaminants is almost endless and can include food, pulp, waste, or other substances. Afterwards, the water requires further scrubbing, with the aid of bacteria. It is in this part of the process that compressed air (ideally provided by energy-efficient rotary lobe blowers) plays a vital role.

Industrial vacuum systems are a challenge to optimize. They have more distribution system variables to balance than a compressed air system does. Vacuum systems conveying particulate are sensitive to velocity. If the velocity is too high, pressure drop results. If it’s too low, particulate doesn’t stay in suspension, and there can be compliance and safety problems. For instance, when conveying wood or other explosive dust, dropping below “critical” velocity allows dust to accumulate in the bottom of the duct, creating an explosive hazard. Entire plants have burned to the ground, and lives have been lost due to these types of incidents. According to OSHA¹, wood is not the only explosive material in dust form.

A facility audit examined the plant electrical energy consumption to find ideas to reduce plant energy use while meeting the process demand. Based on discussions with plant staff and a brief review of the process, it was decided to focus the effort on reducing the electrical energy required to provide aeration air to the secondary activated sludge process. The aeration air blowers were the largest consumers of electrical power in the plant and significantly less efficient than the newer blowers that have been introduced to the market place in the recent years.