Leaks are a significant source of wasted energy in a compressed air system, often wasting as much as 20%-30% of the compressor’s output. Compressed air leaks can also contribute to problems with system operations, including:

• Fluctuating system pressure, which can cause air tools and other air-operated equipment to function less efficiently, possibly affecting production

• Excess compressor capacity, resulting in higher than necessary costs

• Decreased service life and increased maintenance of supply equipment (including the compressor package) due to unnecessary cycling and increased run time.

Although leaks can occur in any part of the system, the most common problem areas are couplings, hoses, tubes, fittings, pipe joints, quick disconnects, FRLs (filter, regulator, and lubricator), condensate traps, valves, flanges, packings, thread seal-ants, and point-of-use devices. Leakage rates are a function of the supply pressure in an uncontrolled system and increase with higher system pressures. Leakage rates identified in cubic feet per minute (cfm) are also proportional to the square of the orifice diameter. See table below.

a For well-rounded orifices, values should be multiplied by 0.97 and by 0.61 for sharp ones.

Leak Detection

The best way to detect leaks is to use an ultrasonic acoustic detector, which can

recognize high frequency hissing sounds associated with air leaks. These portable units are very easy to use. Costs and sensitivities vary, so test before you buy. A simpler method is to apply soapy water with a paintbrush to suspect areas. Although reliable, this method can be time consuming and messy.

Example

A chemical plant undertook a leak-prevention program following a compressed air audit at their facility. Leaks, approximately equivalent to different orifice sizes, were found as follows: 100 leaks of 1/32” at 90 pounds per square inch gauge (psig), 50 leaks of 1/16” at 90 psig, and 10 leaks of 1/4” at 100 psig. Calculate the annual cost savings if these leaks were eliminated. Assume 7,000 annual operating hours, an aggregate electric rate of Rs.0.05 kilowatt-hour (kWh), and compressed air generation requirement of approximately 18 kilowatts (kW)/100 cfm.

Cost savings = # of leaks x leakage rate (cfm) x kW/cfm x # of hours x Rs./kWh

Using values of the leakage rates from the above table and assuming sharp-edged orifices:

Cost savings from 1/32” leaks = 100 x 1.46 x 0.61 x 0.18 x 7,000 x 0.05 = Rs.5,611

Cost savings from 1/16” leaks = 50 x 5.72 x 0.61 x 0.18 x 7,000 x 0.05 = Rs.10,991

Cost savings from 1/4” leaks = 10 x 100.9 x 0.61 x 0.18 x 7,000 x 0.05 = Rs.38,776

Total cost savings from eliminating these leaks = Rs.57,069 Note that the savings from the elimination of just 10 leaks of 1/4” account for almost 70% of the overall savings. As leaks are identified, it is important to prioritize them and fi x the largest ones first.

Compressed air generation is one of the most expensive utilities in an industrial facility. When used wisely, compressed air can provide a safe and reliable source of power to key industrial processes. Users should always consider other cost-effective forms of power to accomplish the required tasks and eliminate unproductive demands. Inappropriate uses of compressed air include any application that can be done more effectively or more efficiently by a method other than compressed air. The table below provides some uses of compressed air that may be inappropriate and suggests alternative ways to perform these tasks.

*Equipment that is temporarily not in use during the production cycle.

**Equipment that is no longer in use either due to a process change or malfunction.

Example

The table below shows inappropriate uses of compressed air in an automobile assem-bly plant. The plant took several action steps identified in the table to eliminate or reduce these inappropriate uses. Peak flow is identified in cubic feet per minute (cfm).

The plant audit showed that the energy used to generate the compressed air averages 18 kW/100 cfm. The aggregate electric rate at the plant is Rs. 0.05 per kWh.

Annual savings = [kW per cfm] x [cfm savings] x [# of hours] x [Rs.  per kWh] = 18/100 x [(150 x 6,500) + (1,000 x 5,000) + (800 x 3,500) + (750 x 3,500)] x Rs. 0.05 = Rs. 102,600

Net savings: Calculate electric energy costs for the motor-driven vacuum pump, fans, and actuators, and subtract these costs from the annual savings calculated to determine the net savings. Note that there will be a one-time cost of installation for the added equipment.

Most industrial facilities need some form of compressed air, whether for running a simple air tool or for more complicated tasks such as the operation of pneumatic controls. A recent survey by the U.S. Department of Energy showed that for a typical industrial facility, approximately 10% of the electricity consumed is for generating compressed air. For some facilities, compressed air generation may account for 30% or more of the electricity consumed. Compressed air is an on-site generated utility. Very often, the cost of generation is not known; however, some companies use a value of 18-30 cents per 1,000 cubic feet of air.

Compressed air is one of the most expensive sources of energy in a plant. The over-all efficiency of a typical compressed air system can be as low as 10%-15%. For example, to operate a 1-horsepower (hp) air motor at 100 pounds per square inch gauge (psig), approximately 7-8 hp of electrical power is supplied to the air compressor. To calculate the cost of compressed air in your facility, use the formula shown below:

Cost (Rs.) = (bhp) x (0.746) x (# of operating hours) x (Rs/kWh) x (% time) x (% full-load bhp) / Motor Efficiency

Where:

bhp—Motor full-load horsepower (frequently higher than the motor nameplate horsepower—check equipment specification)

0.746—conversion between hp and kW

Percent time—percentage of time running at this operating level

Percent full-load bhp—bhp as percentage of full-load bhp at this operating level

Motor efficiency—motor efficiency at this operating level

Example

A typical manufacturing facility has a 200-hp compressor (which requires 215 bhp) that operates for 6800 hours annually. It is fully loaded 85% of the time (motor efficiency = .95) and unloaded the rest of the time (25% full-load bhp and motor efficiency = .90). The aggregate electric rate is Rs.0.05/kWh.

Cost when fully loaded = (215 bhp) x (0.746) x (6800 hrs) x (Rs.0.05/kWh) x (0.85) x (1.0) / 0.95 = Rs. 48,792

Cost when unloaded = (215 bhp) x (0.746) x (6800 hrs) x (Rs.0.05/kWh) x (0.15) x (0.25) / 0.95 = Rs. 2,272

Annual energy cost = Rs. 48,792 + Rs.2,272 = Rs. 51,064

PETplanet Insider December 2010 Cover Page

Survey - Compressor Manufacturers for PET Blowing

Survey - Compressor Manufacturers for PET Blowing

It is with great pride that we announce the publication of our organization’s name in the prestigious PETplanet Insider magazine, the leading publication for the PET industry in their survey of compressor manufacturers for PET blowing. Our organization’s name has been published side by side with other industry juggernauts which is a source of great pride to us.

We thank everyone who has been with including our partners, suppliers and customers who have made this day possible.

The Aeroflon Team

In our previous post,you came to know how single stage reciprocating air compressor works.The working principle of air compressor is same in all types of reciprocating air compressor.The difference is in stages of compression, construction, cooling media etc. This post will give you clear idea of working principle of Double Stage Reciprocating Air Compressaor.

Double stage reciprocating air compressor consist of two cylinders. One is called LOW PRESSURE CYLINDER and another is called HIGH PRESSURE CYLINDER.When piston in low pressure cylinder is at it’s outer dead centre (ODC) the weight of air is zero (neglecting clearance volume), as piston moves towards inner dead centre (IDC) pressure falls below atmospheric pressure and suction valves opens due to pressure difference.The fresh air is drawn inside the low pressure cylinder through air cleaner.This air is further compressed by piston and pressure inside & outside the cylinder is equal, at this point suction valves closed.As piston moves towards ODC compression of air took place and when the pressure of air is in range of 1.5 kg/centimeter square TO 2.5 kg/centimeter square delivery valves opens & this compressed air is then entered into High pressure Cylinder through INTER COOLER.This called as Low Pressure Compression.If suction and discharge stroke took place on both side of piston then it is called Double Acting Low Pressure Compression.

When air pressure in high pressure cylinder is below to the receiver pressure,suction valves of high pressure cylinder opens & low compressed air from Low Pressure Cylinder drawn into High Pressure Cylinder.As piston moves towards the ODC, this air is further compressed.When air pressure from low pressure cylinder and inside the high pressure cylinder is equal,suction valves closed.Now air is further compressed by piston untill the
pressure in the High Pressure Cylinder exceeds that in the receiver & discharge valves opens.This desired high pressure air is then delivered to receiver.Same procedure is repeated in every cycle of operation.If suction & discharge stroke took place on both side of piston then it is called Double Acting High Pressure Compression.In Double Stage Reciprocating Air Compressor AIR PRESSURE can be developed in range of 5.5 kg/centimeter square TO 35 kg/centimeter square.

Normally where we require AIR PRESSURE above 7.0 kg/centimeter square & delivery of air above 100 cubic feet/min. this DOUBLE STAGE RECIPROCATING AIR COMPRESSOR is used. This is most common model
used in various plants.

Posted by: The Aeroflon Team

In single stage reciprocating air compressor the entire compression is carried out in a single cylinder.If the compression is affected in one end of the piston & cylinder then it is known as Single Acting & if the compression is affected in both ends of piston & cylinder then it is known as Double Acting reciprocating air compressor.

The opening & closing of simple check valve (plate or spring valve) is depend upon difference in pressure,if mechanically operated valves are used for suction & discharge then their functioning is controlled by cams.Now come to main point “How Single Stage Reciprocating Air Compressor Works?” The weight of air in the cylinder will be zero when the piston is at top most position,if we neglect clearance volume.When piston starts moving downwards,the pressure inside the cylinder falls below atmospheric pressure and suction valve/inlet valve opens.The air is drawn into the cylinder through air cleaner (SUCTION STROKE).

When piston moves upwards,compresses the air in cylinder & inlet valve closes when pressure reaches to atmospheric pressure. Further compression follows as the piston moves towards the top of its stroke until,when the pressure in the cylinder exceeds that in the receiver. (COMPRESSION STROKE.)

At the end of this stroke discharge/delivery valve opens & air is delivered to receiver for reminder of the stroke. (DISCHARGE STROKE)

When it is double acting reciprocating air compressor,suction stroke is in process at one end of piston while at same time discharge stroke is in process at other end of piston. In simple word we can say that suction & compression took place on both end of piston & cylinder in double acting reciprocating air compressor.

The working of Double Stage (Two Stage) reciprocating air compressor will be describe in next post.

Posted by: The Aeroflon Team

Factors that affect Cylinder Lubrication

Inlet Gas Debris – Even when the proper rate and lubricating medium are in use, dirt and foreign matter in the gas will prevent the lubricant from performing properly. Inlet gas debris screens with a maximum 50-micron mesh opening are recommended. Proper maintenance of inlet screens is required to minimize pressure losses in the inlet piping and between stages.

Excessive differential pressure is the best indicator of a plugged screen. Removal of the screen, cleaning and re-installing is absolutely critical to ensure as much as possible that all debris is collected and removed. Removal of a plugged screen without cleaning and re-installing it will allow debris directly into the cylinder and should never be practiced.

Oil Dilution – Cylinder lubrication requirements will vary with the operating conditions and the composition of the gas to be compressed. Careful consideration must be given to proper cylinder lubrication selection. The degree of cylinder oil dilution by the process gas stream is influenced by the following factors: process gas composition and specific gravity (SG) – usually the higher the SG, the higher the pressure, the greater the oil dilution; discharge gas temperature – the higher the cylinder discharge temperature, the less the oil dilution; lubricant selection – some types of oil are more prone to dilution than others; CO2 or H2S content – these two components will compound the dilution effects of the gas and create acidic conditions in the cylinders.

Liquids in Gas – The use of higher viscosity lubricants or specially compounded lubricants can compensate for the presence of liquids in the gas stream. When there are liquids present in the gas, the most effective lubrication of the cylinders and packing required removal of the liquids before the gas enters the compressor.

An interesting point to note is that if there is a small amount of liquid in the gas stream, it will go to one specific point in the compression system. In a plant with several compressors, a small liquid problem may cause a lubrication problem on one compressor but not the one next to it.

Source: An Overview of Compressor Lubricants and Compressor Lubrication, Lingel, Clinton D.

Posted by: The Aeroflon Team