FEATURE COMPRESSED AIR
SMALL COMPRESSORS with big savings potential
Industry has long needed a compact, clean air compressor operating at very high efficiency. Olly Dmitriev, CEO of Vert Rotors explains a new conical rotary design which does the job
F
ood and drink production facilities and pharmaceutical manufacturing plants
require compressed air free from oil contamination in order to comply with regulations and protect sensitive equipment. ISO 8573-1 classifies the quality of air based on oil content in classes 0 to 4. Class 0 is completely free of oil while Class 1 will contain less than 0.01 mg oil per m3 of air. Using filtration in oil-injected
compressors has proven to be inefficient in achieving a high degree of air purity. The presence of multiple filters decreases efficiency, increasing power consumption, installation and associated maintenance costs. While filter performance is often specified at 20°C, an increase in temperature to 40°C can reduce its lifetime from 1000 hours to 50. The concentration of oil particles may increase to 20 times the design value. It’s essential to improve energy efficiency for the whole system while standalone large compressor units can be highly efficient, according to US Department of Energy; leakages in air pipes can waste about 20% of total capacity. This means that in some cases it is better to install multiple smaller compressors locally.
DRY-RUNNING OR INJECTION OF LIQUID? Typically, manufacturing facilities run centralised ‘compressed air plants’ producing a massive supply. However, if compressors are placed locally we can get away with flow rates of 100-300 l/min. Currently such rates are achieved with dry-running piston or scroll compressors.
However, piston compressors produce noise and vibrations and are less reliable. The scrolls generate very little noise and have proven to be a preferred solution for small applications. The problem in dry- running (adiabatic) operation is that compression generates a lot of heat, leading to loss of efficiency and more kWs used to produce the required volume or air. By achieving 9 bara, dry-running compressors discharge very hot air with temperature of up to 200°C. Twin screw rotary compressors with
water injection are quieter and very efficient. Until recently the smallest available machines were large units producing 1300 L/min and using 15kW of power; good for a central compressor plant but oversized for a local supply. In small sizes twin-screw technology does not achieve high efficiency because water is a poor lubricant, unable to seal clearance between the rotors and the housing (the kinematic viscosity of water is 80 times lower than machine oil) and high pressure air leaks back. We developed a small conical screw
compressor operating with water injection. Tests have shown it maintains 95% volumetric efficiency, producing 220 L/min under the load of 9 bara and using 2.5kW. Clearly, an ideal machine for a local supply of clean air. According to Worthington Creyssensac, water-injected compressors use about 20% less energy than ones that run dry as water-lubricated machines are more efficient. The heat generated is absorbed by the liquid, removing the need for after-cooling.
DRYER SAVES ENOUGH TO PAY FOR ITSELF IN 1 YEAR
Gardner Denver distributor Aircare Compressors has helped plastics company BPI Heanor replace 10 point- of-use purged desiccant dryers with just one CompAir A488TVT Zero Purge desiccant dryer, saving enough energy to pay for itself in just one year. The BPI site recycles used polythene bags into refuse sacks. It uses large amounts of compressed air in its production process but this air has to be extremely dry as any water that condenses out under pressure can cause problems with the equipment. The 10 separate point-of-use purge driers were each capable of drying 100-165 cfm at 7 bar(g). However, after a survey Aircare engineers found that they could replace these with a single CompAir Zero Purge
18 DECEMBER/JANUARY 2017 | FACTORY EQUIPMENT
desiccant dryer which was capable of meeting the site’s requirements all by itself. “The CompAir dryer is much more efficient and as the dryers operate for 24 hours a day, 360 days a year, even a small increase in reliability and efficiency can make a real, positive impact on costs,” comments sales engineer Steve Flint. Likely to have a payback period of only one year,
the new dryer was sized to accommodate extra capacity if BPI expands the site in the future.
Gardner Denver
01527 838200
www.gardnerdenver.com
CASH SAVINGS It is well known that electricity makes up 70-80% of the lifetime cost of a compressor (the rest is installation, servicing and decommissioning). Reducing energy bills 20% by cutting transmission losses then a further 20% by improving energy efficiency with water-injection would dramatically reduce the overall bill - but is it possible? In the oil-injected market high efficiency at reasonable cost has been provided by screw rotary compressors. These have become the dominant option, holding 56% market share. Water-injection has yet to replicate this success. To operate with water twin-screw compressors have to be re-engineered from corrosion-free materials at great expense. Consequently, for economic reasons
only larger water-injected screw compressors starting from 15kW (more typically 50-75kW) have been readily available. For example, Atlas Copco’s water injected twin-screw compressors start from AQ 15 VSD (15kW), CompAir’s smallest machine is D15H (15kW) while Aerzener offers a machine with water injection running at 75kW.
SMALL WATER INJECTED COMPRESSOR Vert Rotors presented a small 2 kW oil- free screw compressor running with water injection at 13th European Fluid Machinery Congress in October 2016. Tests have demonstrated energy
efficiency of the oil-free 2 kW conical screw package (VERT.80) was similar to the level achieved by oil injected twin- screws; the size of the fully-functional floor-mounted package was 60% smaller than a comparable twin-screw; noise levels of 68dB(A), similar to oil- injected twin-screws; and discharge air temperature of 35-40°C. While an emerging technology, the conical compressor has already gained international interest, providing the solution for customers requiring an efficient, low noise source of clean air.
Vert Rotors T: 0131 664 0080
www.vertrotors.com
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