A large food manufacturing operation in the U.S. Midwest spends $529,000 annually on energy to operate the compressed air system.
The plant currently has two supply-side systems that operate and feed two different distribution networks at two different pressures. One compressed air system is at 115 psig (medium pressure system) and the low-pressure system is at 30 psig. The compressed air equipment for both systems is located in four areas throughout the facility.
A significant manufacturing operation, in the U.S. Midwest, had successfully deployed a compressed air leak management program. This on-going leak management program, along with tuning the air compressor control system, had delivered energy savings and a more reliable compressed air system.
In this article, we will provide detail on the characteristics of the baseline system and then share the energy-saving work identified in two projects. These two projects represent work which can be performed by the maintenance teams in every plant. These are also project opportunities we find in almost every plant we visit. The two projects are to (1) repair/replace condensate drains wasting compressed air and (2) to perform a compressed air leak survey.
There were two situations brought to our attention. The first was that production at times was having to slow down, or even stop, due to compressed air system pressure falling below the required levels. The second reason was due to reports, from plant personnel, of compressed air moisture problems negatively affecting the bag life of the dryer baghouses.
In order for a compressed air system to be designed properly, altitude must be taken into consideration. In order to calculate the demand profile, tool air consumption must also be adjusted for altitude.
Just as many ambient air issues with regard to the actual equipment operating environment are created by personnel and can be corrected by personnel, inlet air contamination is always created by humans and there is almost always a correction that will either eliminate the issue or mitigate the effect.
A zinc producer spends an estimated $516,000 annually on electricity to operate the air compressors in a compressed air system at its north American plant. The current average electric rate, at this plant, is 5 cents per kWh, and the compressed air system operates 8,760 hours per year. This system assessment recommended a group of projects able to reduce these energy costs by fifty-one percent (51%) to an annualized $270,000. The simple payback of the project was 15 months – without taking into account potential incentive dollars from the local utility.
This plant has three production lines producing snack food. Depending on the time of year and production demand the plant can operate anywhere from no production lines to all three production lines. A thorough supply and demand-side system assessment was done at this plant. This article will focus on some recommended demand-side reduction projects including nitrogen generation, air vibrators, leaks and vacuum venturis.
Annual plant electric costs for compressed air production, as operating today, are $147,469 per year. If the electric costs of $750 associated with operating ancillary equipment such as dryers are included, the total electric costs for operating the air system are $148,219 per year. These estimates are based upon a blended electric rate of $0.087 /kWh. The air system operates 8,760 hours per year. The load profile or air demand of this system is relatively stable during all shifts. Overall system flow ranges from 800- 1,000 acfm during production. The system pressure runs from 95 to 80 psig in the headers during production.
A complete compressed air system assessment should provide detailed information on both the supply and demand sides of the system. The supply-side refers to the equipment supplying compressed air – the air compressor, dryers, filters, piping and storage tanks. The purpose of this article is to illustrate what information we believe a factory should receive from a supply-side system assessment and more importantly – what information a plant should always know about their compressed air system.
A chemical plant spends an estimated $587,000 annually on electrical energy to operate their compressed air system. In addition, the plant has an expenditure on rental air compressors of equal or greater size - but this will not be covered in this article. The plant was built in the 1940s and modernized in the 1970s. The plant generates its own power and serves many processes. The average cost per kWh is $0.0359.
A pharmaceutical product manufacturer spends an estimated $137,443 annually on electricity to operate the oil-free air compressors in its compressed air system. The compressed air system operates well and is providing the level of purification required. Our team visited the plant and identified a group of projects which could reduce compressed air demand and reduce energy costs by $42,248 – or 31% of current use.
A plastic product manufacturer spends an estimated $245,000 annually on electricity to operate the air compressors in a compressed air system at its plant located in a midwestern U.S. state. The main manufacturing process is plastic extruding. The current average electric rate, at this plant, is 7 cents per kWh. The compressed air system operates 8,760 hours per year and the load profile of this system is relatively stable during all shifts.
A major poultry processor and packager spends an estimated $96,374 annually on energy to operate the compressed air system at its plant located in a southern U.S. state. The current average electric rate, at this plant, is 8 cents per kWh.
A centrifugal air compressor operates over a range of flows and discharge pressures. The operating performance curve is shaped by the selected individual internal components and affected by operating conditions such as inlet pressure, inlet temperature, and cooling water temperature. The process of dynamic compression, as applied in a centrifugal compressor operating stage, is velocity and kinetic energy converted to pressure and temperature as the flow is restricted. Another term for this process is mass flow – the power requirement to deliver the rated cfm of flow at the rated pressure (psig) is determined by the weight of the air.
Quite often the typical variability in compressed air flow demand does not proportionately translate into power reductions at the air compressors. This can be a result of numerous problems with the compressed air supply system. It is important to understand the supply-side’s ability to respond to the demand-side of the compressed air system. If the air compressors, on the supply-side, are not able to translate flow reductions into energy savings, implementation of demand reduction projects should be re-evaluated.
In general, this article focuses on the definitions of terms often used to understand centrifugal air compressor performance. Comments are also made on how to measure power consumption. This article is not intended to be an engineering discussion of the various types and designs of centrifugal and other air compressors.
Compressed air has moved to higher visibility in the energy conservation field, and the buzzwords abound: “the fourth utility” — “your most expensive utility” — “eight times more expensive than electricity” — “a quarter-inch leak costs $9,000 in wasted energy.” This greater awareness has also produced compressed air auditors that are springing up like summer dandelions. With audits available from many sources, it is important to understand what plant operations, engineers and maintenance managers should expect from a complete audit — or more aptly — a complete air system review.
This metal fabrication and machining facility produces high-quality precision-built products. Over the years, the plant has grown and there have been several expansions to the current location. The company currently spends $227,043 annually on energy to operate the compressed air system. This figure will increase as electric rates are raised from their current average of 9.8 cents per kWh.
This is a food processing plant where processes and standards are controlled by FDA to AIB standards. Annual plant electric costs for compressed air production, as operating today, are $116,765 per year. If the electric costs of $3,323 associated with operating ancillary equipment such as dryers are included, the total electric costs for operating the air system are $120,088 per year. These estimates are based upon a blended electric rate of $0.085/kWh.
Over many years of reviewing industrial compressed air production machinery, of many types and styles, there is one common thread or complaint; “push-to-connect pneumatic tubing connections/fittings are a continual source of compressed air leaks and production interruptions.” Probably seventy-five to eighty percent of push-to-connect type tubing fittings use flexible tubing selected for lower material cost and assembly rather than an alternate appropriate hard metallic tubing.
Based on the air system operating 8,760 hours per year, the group of projects recommended below could reduce these energy costs by an estimated $170,718 or 56% of current use. In addition, these projects will allow the plant to have a back-up compressor and help eliminate the rental expenditure for compressor maintenance or downtime.
This food & beverage plant is a large (500,000 sq ft) meat processing plant with twenty packaging lines and nine palletizers. The compressed air system is supplied from three separate rooms with seven individual lubricant-cooled, single and two-stage rotary screw compressors. The plant has four blower purge desiccant dryers designed to deliver a - 40°F pressure dewpoint.
This glass bottle production plant had a complete compressed air audit in 2001 and 2002 at which time many successful projects reduced and stabilized the demand at 3,148 scfm at 95 psig for the high pressure system air and 9,300-9,500 scfm at 58 psig for the low pressure system. Successful application of an oversized 7,200-scfm rated cycling refrigerated dryer completely dried up the high-pressure air, allowing the removal of several non-performing desiccant dryers and savings in direct kW and purge air.
This was a complete supply and demand-side system assessment. The supply-side audit involved shutting off old air compressors and purchasing newer more efficient air compressors and dryers. The demand-side audit involved finding ways to improve the piping and reduce compressed air consumption.
Annual plant electric costs for compressed air production, as operating today, are $3,050,625 per year. If the electric costs of $27,811 associated with operating ancillary equipment such as dryers are included the total electric costs for operating the air system are $3,078,436 per year.
