Industrial Utility Efficiency

# Air Storage Receiver Helps Dense-Phase System

System Assessment of the Month
Where: Georgia
Industry:

Ceramics Processor

Issue:   Periods With Insufficient Air Pressure
Audit Type:  Supply-Side Compressed Air Storage

### The Problem

Sitting on his desk the day Brian began his new job as Plant Engineer for Carbo Ceramics’ McIntyre, GA facility was a proposal to purchase a new 150 HP air compressor as a backup machine. The facility already had six of these machines and, yes, all six ran almost continuously. A rental unit was already on site and “installed” as a backup, just in case a permanent machine failed. The new compressor was intended to replace that rental. Brian had worked with me (the author-Brent Ehrlich) together on a couple of projects in the past and had learned enough from those projects to recognize that nowhere did the proposal state that the existing compressors were being used efficiently. Nor did the proposal identify the problem a new compressor would solve. There was only a mention of the symptoms: all installed compressors ran continuously, and pressure was unstable, fluctuating as much as 25 PSI. The source of these symptoms was not evident. It might be on the demand side, in the compressor controls, or reflect a real lack of capacity. Brian suspected that if the underlying problem was understood, the existing compressors could be used more efficiently, allowing one of them to be turned off and used as the backup compressor.

Carbo Ceramics, McIntyre, Georgia Facility

To identify the problem, we needed more data. We needed a thorough understanding of how compressed air was being applied. The data presented to support the purchase of a new compressor showed the amperes used by each compressor, with a separate trend for each. This showed that all compressors remained on-line continuously (or nearly so), but it also revealed that multiple compressors were simultaneously running at part load, an indication of inefficient operation. My guess was that production events creating significant peaks in demand were causing all six compressors to load. When the events ended, some would unload and run unloaded until the next event occurred. But nothing was known about these peaks, or even if they existed at all. How much air (volume) was involved? What did the flow profile (rate and magnitude of change) look like? What was the maximum flow rate? How long did the events last? What were the actual pressure requirements? My goal was to provide Brian with a clear picture of production’s needs so that he could make an informed decision.

Compressors make flow. Production demands flow. So if we want to match compressor horsepower (supply) with the demand, shouldn’t we measure flow? As we all know, we can’t manage what we don’t measure, so we jolly well had better measure something! Having received the same training in flow measurement that NASA engineers get I tend to favor measuring this parameter, however, similar information can be obtained from data for kW, amps, or pressure. AirMaster+ software, available from the D.O.E., will even correlate flow to load/unload cycle times.

### Question: Buy a new air compressor or install storage capacity?

Scenario #1: Buy a New Air Compressor: Scenario #2: Install Storage Capacity & Modify Controls
Capital Costs: $50,000$123,000
Power & Maintenance Cost Increase*: $40,600 - Power & Maintenance Cost Decrease*: -$81,200
1 Year Cost Increase: $90,600$41,800
5 Year Cost Increase: $253,000 - 5 Year Cost Decrease: -$283,000