Printing Facility Reduces Air Demand and Avoids a \$34,000 Capital Expenditure
This article will focus on a compressed air system assessment done at a printing facility in Canada. The energy costs at the time, in Manitoba, were \$0.025 per kWh and the installation was of just 65 horsepower of air compressors. The compressed air demand was very high on the system which was causing pressure problems and as a result the company was planning the purchase of a new 50 hp air compressor and air dryer to meet demand.
|"Total energy savings were \$23,800 per year."
- Ron Marshall, CET, CIM, Manitoba Hydro
The portion of the system assessment we will review is the work done to understand the demand profile and constituents of compressed air demand. The results were significant in that they not only reduced air demand, but more importantly in this case, helped the facility NOT to have to purchase an additional air compressor. Purchasing an additional air compressor would have created an unnecessary \$34,000 capital expenditure. Further to this, the study also helped identify and eliminate electrical demand caused by an boiler style humidification system and avoid proposed air powered humidification load being placed on the compressed air system. Due to space limitations, this article focuses only on the “constituents of demand” segment of the compressed air system assessment.
Constituents of Compressed Air Demand
The plant had two lubricated rotary screw type compressors and refrigerated dryers installed; one 50 horsepower (hp) and one 15 hp unit. In general, the piping system consisted of a mixture of loop and radial feeds appearing to be adequately sized, in most instances, based on pressure logger data collected during the study.
A detailed end use assessment was performed to determine the makeup of the compressed air demand. Some of this demand was deemed as "inappropriate use" that could be reduced or eliminated by applying efficiency measures. The following is a constituents of demand table which takes into account the potential reductions in air demand identified during the plant study. The demand reductions were to be achieved by reducing blowing and by eliminating existing humidification load and other poor air demands.
Table 1: Constituents of Compressed Air Demand
Compressed air is commonly used to supply equipment and machines in a standard industrial plant. Many times the machines are used for only a small portion of the day, yet the air system must continue to feed these idle machines. A number of machines in the plant were observed standing idle, but with significant air demand. It was estimated that 10 cfm of plant air load was attributed to these machines. Estimated energy conumption for this load was calculated to be 18,000 kWh costing \$1,674 per year.
High Pressure/Low Pressure Blowing
Compressed air is sometimes used to move or position material in process machines to aid in proper operation of the device. Many times these applications require low pressure high volume air streams. Using high pressure plant air for these application is expensive since a large amount of energy is expended in compressing the air to high pressures, only to have it expanded down again to lower pressures. As an example of the difference in energy requirements, a regenerative blower can produce 220 cfm around 2 psi at 12 HP. A similar 100 psi screw compressor producing 220 cfm would consume 55 HP.
|"Replacing the boiler system with a high-pressure water system saved 482,900 kWh." - Ron Marshall, CET, CIM, Manitoba Hydro|
In this case, because the compressed air system was heavily loaded at times due to so, compressed air powered humidification nozzles, these high volume blowing applications took needed air demand from the system and caused low system pressures, in turn affecting production machines. This being the case, the following high pressure demands were identified as loads that could be converted to low pressure blowing:
- The Perfect Binder operators were using high pressure air to prevent paper jams when binding cookbooks requiring single page inserts. Whenever this happened low pressure problems occurred in the plant. This application was measured at 40 cfm peak. This blowing was being done because a regenerative blower has failed and a replacement was not forthcoming. Replacement of the blower was recommended as soon as possible.
- The paper cutter in the sheeting area had a blowing device fashioned from a copper pipe. Holes are drilled in the pipe to provide blowing to position the paper web. This application was measured at 20 cfm. In addition this machine uses flexible nozzles for paper positioning measured at 20 cfm. Low pressure blowing could provide a better solution to this application.
Because these applications were used intermittently the average compressed air and annual kWh consumption associated with the applications was not all that significant, however, the impact on the system pressure was a concern. Addressing these application helped defer the purchase of an additional air compressor.
Humidification systems are commonly seen in plants in Manitoba that have large ventilation systems. Printing plants need this ventilation due to remove ink fumes. Since the ventilation return air is taken from outdoors the extremely cold weather in winter months makes the ambient plant air very dry. The humidification systems add water to the air and reduce problems associated with static charges and drying/shrinkage of raw materials. Common varieties of systems use steam, compressed air and high pressure water to add moisture to the environment. Costs associated with the systems vary widely. The most expensive energy consumer is the steam system with energy intensity of about 340W per lb of water added, and the least expensive is the high pressure water system with energy ratings of about 1W per lb. The compressed air powered system installed in the sheeting and Heidelberg area of the plant (24 nozzles at 1.8 cfm per nozzle) was consuming 43 cfm with annual costs of \$2,399 per year. Converting these existing systems to high-pressure water was projected to reduce air demand by 43 cfm
A further examination of existing electric boilers operating throughout the plant showed that their total energy consumption was 486,900 kWh per year. These systems were slated for conversion to compressed air powered nozzles. Replacing them instead with a high-pressure water system was projected to eliminate future compressed air cosumption by 59,000 kWh and avoid further compressed air demand. Total energy savings of the final conversion would be worth an estimated \$30,000 per year – plus the cost avoidance of adding a new air compressor.
Energy Savings and Cost Avoidance
Reducing the constituents of demand played an important role in reducing the compressed air energy consumption by 115,000 kWh. Replacing the boiler system with a high-pressure water system saved 482,900 kWh. Total energy savings were \$23,800 per year. Deferring the purchase of the new air compressor avoided a \$34,000 capital expenditure.
Note: Savings due to conversion of the existing units are included in the air system calculations
Many owners of compressed air systems with less than 100 horsepower of installed capacity do not think they can achieve substantial savings with a compressed air system assessment.
Whenever a “smaller” system is at its’ limit and a new compressor purchase is being planned, we highly recommend a system assessment before making any decisions. This printing facility received an unexpectedly positive result from the assessment, which helped their financial performance.
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