Industrial Utility Efficiency    

Compressor Controls

A large mining complex in a remote northern region of the world invited a compressed air auditor in to assess the efficiency of a problematic system. Site personnel and their air compressor supplier were concerned a system in one of the buildings was not running optimally, and wanted to know what size of compressor to install in the facility. The auditor found significant savings in this target system, but even larger potential savings were found in other ancillary systems in the complex, as part of an extra investigation conducted while at the site. Overall, the potential energy savings total more than half of a million dollars, if all recommendations are implemented.
Great Plains has carved a global reputation for producing world-class seeding equipment since it first opened its doors in 1976. Great Plains manufactures a range of products from grain drills and planters, to compact drills and tillage equipment. They have established an international business built on expertise, knowledge and a commitment to producing products meeting the rigorous demands of the agricultural sector.
Load-sharing is an important part of a multiple centrifugal-compressor master control system. It minimizes blow-off based on the available turn-down. In addition, remote start-stop saves more energy if load floats between different ranges. Finally, adding a screw compressor and implementing a hybrid control system might save the most energy and provide the best back-up. In any case, a well-instrumented system allows engineers and operators to assess, optimize and tune the system.
When a system has the right combination of VFD and base-load air compressors, how do you coordinate their control? What tells the air compressors to run and load, to have just enough (or no) base-load air compressors and a VFD running, all the time air is needed? Appropriate master controls are needed. These controls are often called “sequencers” or “master control systems”.
It is becoming a “best practice” to install a variable frequency drive (VFD) air compressor whenever one is replacing an old air compressor.  As a result, real systems have fixed-speed and VFD air compressors, mixed.  I have observed several VFD compressor sizing methods.  In my last article, I referred to a common method: size one VFD compressor for the whole system.  This can work.  However, if it doesn’t meet a higher peak demand, one or more of the old compressors will be started, and a mixed system results.   Another method is to replace a compressor with the same size, but with a VFD.  If the compressor that was replaced is large, a big VFD is installed.  If small, a small one.
A newly constructed ethanol plant experienced control gap issues shortly after comissioning.  This article discusses the cause of the issue and how the problem was solved.
Facility managers, how would you like the peace of mind from knowing the system you had installed or modified is thoroughly tested - to the same degree as a new production line?  How would you like to be confident that the money you spent is still paying back benefits, year after year? 
“Retro-Commissioning” (ReCX) of compressed air systems has become a trendy activity with many utility demand-side-management programs emerging in the last 5-10 years.  This is intended to be the process of “tuning up” a compressed air system, getting low cost savings from mostly adjustments and repairs.  The term was borrowed from the building/HVAC industry, where it means to get a system operating as it was originally “commissioned”. 
UniFirst is one of North America’s largest workwear and textile service companies. They outfit nearly two million workers in clean uniforms and protective clothing each workday. Founded in an eight-stall garage in 1936, the Company has grown to 240 customer servicing locations throughout the U.S. and Canada servicing 300,000 business customer locations. The subject of this article is an energy-saving Air Demand Analysis (ADA), conducted by Kaeser Compressors, at UniFirst’s centralized 320,000 square foot hub Distribution Center located in Owensboro, Kentucky.
MHPSC Canada is a large facility specializing in machining and manufacturing large pieces for power generation (gas turbines, large hydro, wind) and deep sea oil and gas operations.  Smaller machining and manufacturing are also done in the facility, as well as welding and piping fabrication. MHPSC purchased flow meters for two systems, the Large and Small Machine Shops, to measure the total compressed air production.  Since the two systems have piping that is physically close together, it was felt that there was an opportunity to tie the two systems together to save energy.  The readings showed that the compressed air demand was indeed low enough in the two systems to enable a 100 hp VFD compressor to feed the combined systems.
Compressed air optimization measures adopted by PTMSB have reduced the consumption of compressed air by 31 percent resulting in savings of about 3,761,000 kWh per year in energy consumption. The monetary savings are MYR 1,090,627 per year ($255,000 USD). The CO2 reduction is estimated at 2,735 ton per year.