Industrial Utility Efficiency

# Compressed Air Piping Changes Help Dairy Producer Optimize

### Introduction

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.

There are actually two compressed air systems, one serves “the Dry Side” of the plant and one is dedicated to “Plant Air”. The main purpose of this project is to examine combining the two systems into one by making piping and valving changes. By running a single system at today’s current demand of 946 acfm maximum, the annual electric cost for compressed air is \$125,445. By combining the system, the plant could save \$22,024 per year in electric costs.

Table 1: Key Compressed Air System Characteristics – Current System

### Recommended Piping and Storage Project

Combine multiple systems; set up auto shut-off valves with pressure sensors to close valve if pressure drops.

 Electric demand of current air compressor system 28.9 kW Relative gain in efficiency 15% Annual hours of operation for current unit (new conditions) 8,760 hrs/yr Annual energy savings \$22,029/year Equipment and installation cost for new unit including tanks \$40,000

Increase compressor room piping size to six inch, for the collection header, and add two x 2,000 gallon storage tanks outside of Compressor Room 2 to help with the future consideration of a smart control system. By adding additional storage it allows units to operate more efficiently, with complete blow down and idle, by allowing the storage to supply peak demands without affecting the overall system. Install an Have auto open valve to tie-in the two systems together on a pressure signal or isolate each system. We recommend utilizing Use a flow based control system and flow meters. Review use of FG oil and other compressors future performance.

Table 3: Key Compressed Air System Characteristics – Proposed System

Figure 2: Proposed Compressed Air System Diagram

### Compressed Air Leak Survey

Most plants can benefit from an ongoing air leak management program. Generally speaking, the most effective programs are those that involve the production supervisors and operators working in concert with the maintenance personnel.

A partial survey of compressed air leaks was conducted at the plant and 22 leaks were identified, quantified, tagged, and logged. Potential savings totaled 56 cfm for the 22 leaks that were identified. We estimate 10 leaks at 3 cfm each of previously tagged leaks, for an additional 30 cfm.

Air Power USA recommends an ultrasonic leak locator be used to identify and quantify the compressed air leaks. We use an Ultraprobe leak detector manufactured by UE Systems. Shutting off or valving off out the air supply to these leaks when the area is idle would save significant energy. use from leaks. Reducing the overall system pressure would also reduce the impact of the leaks, when air to the machine cannot be shut off. Repairing the leaks can save additional energy. The savings estimates associated with a leak management program are based on the unloading controls of the compressors being able to effectively translate less air flow demand into lower cost.

With a few minor exceptions, most of the leaks could not have been found without the use of an ultrasonic leak detector and a trained operator. Leak locating during production time with the proper equipment is very effective and often shows leaks that are not there when idle. However, a regular program of inspecting the systems in “off hours” with “air powered up” is also a good idea. In a system such as this one, some 80 to 90% of the total leaks will be in the use of the machinery, not in the distribution system.

Some of the areas surveyed in the leak study included a great deal of high background ultrasound noise that shields many of the smaller leaks. In continuing the leak management program, plant staff should perform leak detection during non-production hours in order to eliminate some of the high ultrasonic background noise.

Repair all 22 tagged and identified compressed air leaks as well as the 10 already tagged leaks by plant personnel. Continue your ongoing leak identification program.

 Number of leaks 32 leaks Estimated reduction of air flow with proposed project 86 cfm Recoverable savings from air flow reduction \$117.75/cfm yr Annual electric cost savings with proposed project \$10,126/year Unit cost of leak repairs ($25 materials per leak and \$75 labor per leak) \$3,200 Total project cost (materials and installation) \$3,200

Table 4: Compressed Air Leak List

For more information, contact Don van Ormer, Air Power USA, at don@airpowerusainc.com or visit www.airpowerusainc.com.