Industrial Utility Efficiency

An Aging Plant Air System gets a Face-Lift


Does your plant have a ‘mature’ compressed air system with on-going challenges ? If yes, this story may be of interest. It discusses up-grades to the compressed air system in a large manufacturing plant that resulted in significant energy system cost savings, better ownership of the asset by plant personnel and improved production operations.

 

Introduction

The Technical Director of a large facility in the Midwest (producing valves and meters) hired us to assist with a Site Energy & Utility Systems assessment. The compressed air system quickly became one of the main issues identified. The plant was built in the 1960’s and had expanded over the years. Recent reduction-in-force programs (to reduce costs) had impacted the maintenance department and the plant air system was high among the systems that were the most affected. Over the next several months, as management became attuned to all of the air system issues affecting utility costs and process quality concerns, resources were provided and significant improvements occurred.

 

Identification of Opportunities

  • Compressor reliability was low and rentals were being utilized frequently
  • The maintenance program was in need of some technical oversight
  • System pressure was much higher than necessary
  • Motor failures were a regular occurrence - frequent ‘starts’
  • Fouled intake filters and coolers
  • Water in the air lines: Dryers in need of better operational oversight
  • Controls and instrumentation needed up-graded

 

System Description

There were two compressor service rooms, each with two 350 hp rotary air-cooled units. Generally three units were in continuous service near full load on two shifts. Two units operated on afternoon shift and weekends when the Foundry was ‘DOWN’. Minor service items were handled by a small maintenance crew and major repairs were under a ‘Service Contract’ with the equipment supplier. Coordination between the two groups was minimal. Moreover, the Foundry Superintendent (with years of service) had established that the two compressors in his area must be operated at high pressure to minimize casting defects (which we quickly learned were the production bottleneck).

 

Developing a Plan

We installed a 7-day pressure recorder instrument. The main receiver tank at the Foundry compressors would cycle between 106 and 116 psig and the Factory compressors receiver tank at 102 to 112 psig. There was no plant-wide system piping diagram or method to automatically control the air system pressure. Numerous issues had to be investigated.

We visited the plant several times building trust, conducting ‘training sessions’ for the maintenance crew and identifying and prioritizing issues that needed to be addressed. Numerous staff changes may also have been part of the overall challenge. Thus, a few management level reviews were conducted. Our objective was to convince the new engineering and maintenance managers that the system could be upgraded and operate effectively at or below 100 psig without unscheduled outages and ‘rentals’.

We developed a plant air system piping diagram and delineated numerous ‘Demand-Side’ issues. We outlined system conditions, the cost impact upon the plant due to compressor anomalies and how to go about making effective ’change’. Meetings with a representative from the Compressor Service Company resulted in his accepting ‘some’ lack in overall service responsibility, but not the level of support and communications that we had expected. It seemed that the service group enjoyed the frequent repair calls and the sales group wanted to install all new equipment, regardless of distribution and process system issues.

 

Implemented System Changes

  • Two compressors required air-end replacements (near end of life hours)
  • Two motors were replaced with the ‘soft-start’ capability ensured
  • VSD drive was installed on one unit in the foundry
  • The oldest stand-by unit (in poor condition) was replaced with a 200 hp unit
  • ‘Intelligent’ control systems were installed in both compressor rooms
  • Piping changes were made to the main air lines at several bottleneck locations
  • Local surge tanks were installed in the foundry at the sand mold presses
  • Local surge tanks in the factory at the multi-station turret cutting machines
  • New pressure transducers were installed at key points in the system
  • Leak survey: numerous leaks and defective traps were repaired
  • An air dryer service program was developed & implemented

 

Results

System pressure trials confirmed that the compressors could operate effectively at 98 to 102 psig during foundry operation and at 96 to 100 psig when the foundry was down. The VSD unit could generally control the system pressure at 75% load.

Note: Subsequent to start-up and optimization of the new VSD drive and control systems, it was decided to terminate the service contract with the longstanding equipment supplier (due to more performance issues) and hire a regional services company for major services work. The maintenance crew developed a close working relationship with the new vendor.

 

Benefits

  • The plant electric power bill was reduced by an average of \$6,000 per month
  • Emergency rental charges that had averaged \$30,000 per year disappeared
  • Foundry casting operations improved and overtime was reduced
  • Exhaust heat recovery ducts were installed on the compressors (into the foundry) reducing winter building heating costs by \$40,000 per season
  • Cold 700 F make-up air into the foundry was reduced by 40,000 CFM. Employees were much more comfortable

 

Note: Not all projects met the 2-3 year hurdle-rate criteria for industrial energy savings. Some were considered as restoring the integrity of the utility asset. Air-cooled rotary compressors do require a dedicated maintenance program when operating at high pressure in a particulate-laden environment.

 

Summary

If your facility has a ‘mature’ plant compressed air system that has undergone changes over the years and encounters frequent ‘hick-ups’, you may want to consider an overall system assessment by an ‘independent’ expert. Supply-side issues alone generally cannot resolve all of the anomalies with a large plant air system that has evolved over time.

 

Gary Wamsley is an Engineering Consultant at JoGar Energy Services in South Florida with over thirty years of ‘in-plant’ compressed air systems experience. Visit www.jogarenergy.com.

 

For more System Assessment articles, visit www.airbestpractices.com/system-assessments.