Tag: electrical savings

Basics of Compressors

Published on by johnball2014Leave a comment
Single Stage Portable Air Compressor

What is an air compressor?  This may seem like a simple question, but it is the heartbeat for most industries.  So, let’s dive into the requirements, myths, and types of air compressors that are commonly used.  Like the name implies, air compressors are designed to compress air.  Unlike liquids, air is a compressible gas, which means that it can be “squished” into a smaller volume by pressure.  With this stored energy, it can do work for pneumatic systems.

There are two main types of air compressors, positive displacement and dynamic.  The core component of most air compressors is an electric motor that spins a shaft.  Positive displacement uses the energy from the motor and the shaft to change volume in an area, like a piston in a reciprocating air compressor or like rotors in a rotary air compressor.  The dynamic types use the energy from the motor and the shaft to create a velocity with an impeller like centrifugal air compressors.  This velocity converts to a rise in pressure.

How do they work?  Most air compressors are driven by an electric or gas motor.  The motor spins a shaft to push a piston, turn a rotor, or spin a vane.  At the beginning of the air compressor, we have the intake where a low pressure is generated from the displacement to bring in the surrounding ambient air.  Once trapped, Boyle’s law states that when the volume decreases, the pressure increases.  For the dynamic type, the velocity and design will increase the air pressure.  The higher pressure will then move to a tank to be stored for pneumatic energy.  The amount of power required is dependent on the amount of air that needs to be compressed. 

Compressed air is a clean utility that is used in many ways, and it is much safer than electrical or hydraulic systems.  But most people think that compressed air is free, and it is most certainly not.  Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants.  For an electrical motor to reduce a volume of air by compressing it, it takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet (113L) of air every minute to 125 PSI (8.5 bar).  With almost every manufacturing plant in the world utilizing air compressors much larger than 1 horsepower, the amount of energy needed to compress a large volume of air is extraordinary.

Let’s determine the energy cost to operate an air compressor to make compressed air by Equation 1:

Equation 1:

Cost = hp * 0.746 * hours * rate / (motor efficiency)

where:

Cost – US$

hp – horsepower of motor

0.746 – conversion KW/hp

hours – running time

rate – cost for electricity, US$/KWh

motor efficiency – average for an electric motor is 95%.

As an example, a manufacturing plant operates a 100 HP air compressor in their facility.  The cycle time for the air compressor is roughly 60%.  To calculate the hours of running time per year, I used 250 days/year at 16 hours/day for two shifts.  So operating hours equal 250 * 16 * 0.60 = 2,400 hours per year.  The electrical rate at this facility is $0.10/KWh.  With these factors, the annual cost for operating the air compressor can be calculated by Equation 1:

Cost = 100hp * 0.746 KW/hp * 2,400hr * $0.10/KWh / 0.95 = $18,846 per year in just electrical costs.

So, what is an air compressor?  The answer is a pneumatic device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored as pressurized air.  Efficiency in using compressed air is very important.  EXAIR has been manufacturing Intelligent Compressed Air Products since 1983.  We are able to save you money by reducing the amount of compressed air you use.  If you need alternative ways to save money when you are using your air compressor, an Application Engineer at EXAIR will be happy to help you.  We even have a Cost Savings Calculator to find the annual savings and payback period; and you will be amazed at how much money can be saved. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo: Technical Illustration of a portable single-stage air compressor by Brain S. Elliot.  Creative Commons CC BY-SA 4.0

Super Air Knives Save 63% Electrical Cost for a Food Manufacturer Drying Trays

Published on by johnball2014Leave a comment

A food manufacturing company was looking for a more efficient way to dry polypropylene trays that were filled with food product. With their current operation, they would send already packed and sealed food trays through a washing system that used sterilized water. The trays would then have to be dried prior to bulk packaging. The operators would place the trays side by side on a 24” wide open-mesh stainless steel metal conveyor with two or three trays at a time (depending on the tray dimensions). They contacted EXAIR because they wanted to replace their “old and inefficient system” with something better.

In my discussions, they gave some additional details of the operation and the problems that they were seeing. The dimensions of the trays ranged from 150 to 200mm long by 100 to 150mm wide by 35 to 50mm in height. They were cleaning at a rate of 30 trays per minute through the washing and drying system. The washer was designed to recycle the water to improve “green” operations. But the trays were carrying much of the water outside the machine. Thus, they would have to stop and refill the wash system with fresh water.

After the washing cycle, the drying section began. It consisted of two parts; a sponge roller and a heated chamber that would blow hot air. First the trays would run under the sponge roller to absorb the water from the top of the trays. A feature that they did not like was the continuous adjustment to the sponge roller for the different tray heights. They had to make sure that they had good contact without stopping the movement.

Also, with bulk of the water being on top of the trays, the sponge surface would get saturated. They would have to stop the process to change with a dry foam pad or replace due to wear. After the sponge roller, it would move into a heated chamber to remove the remaining portion of the water from the trays. They used a 11 KW heating system to blow hot air. This part of their system required a lot of electricity to run. They wondered if EXAIR could help streamline their process and reduce energy costs.

They sent a photo of their system, reference above. As described, the trays were moving intermittently through the wash cycle and then into the drying operation. When gaps are present in a process, the Electronic Flow Control, or EFC, becomes a great product for energy efficiency. It is designed to use a photoelectric sensor to detect a part and initiate a timing sequence. Using a solenoid valve, it will turn on the compressed air only when needed. With the drying operation, I suggested that they could remove the sponge roller and heated chamber, and replace them with two Super Air Knives. In conjunction with the EFC, we can decrease energy usage, reduce downtime, and increase savings. Profit margins can be critical in the food industry, and EXAIR has many ways to help.

Electronic Flow Control

To expand a bit more about revitalizing the “old and inefficient system” with EXAIR products, I made some suggestions. I recommended two Stainless Steel Super Air Knife Kits, model 110224SS, to be placed near the end of the conveyor. One Super Air Knife would be positioned above the tray to blow across the top; and one would be positioned below the tray under the mesh conveyor to blow across the bottom.

At a slight blowing angle in a counter-flow direction, the air streams would remove the water from the top and bottom of the tray at the same time. This would create a non-contact “wiping” solution. Now they do not have to worry about parts wearing out due to contact. Another unique feature of the Super Air Knife is the strength of the laminar air stream. It is consistent from 3” (76mm) to 12” (305mm) away from the target. Thus, they can easily set the height of the Super Air Knives to dry all the different trays without adjusting it.

And as an added benefit, the water that was being blown off the trays by the Super Air Knives remained within the washing system. The sterilized water was not being wasted and could be recycled. With the Electronic Flow Control, I recommended the model 9056. It is a user-friendly device with eight different timing sequences. They were able to position the photoelectric sensor near the outlet of the washing system. As soon as the trays were detected, the Super Air Knives would turn on to blow two or three trays at the same time. With the EXAIR products installed, the system went from using 11 KW down to 4 KW, a 63% savings.

EXAIR has helped many customers like this one above. When it comes to energy savings, EXAIR leads the way. With two Super Air Knives and an EFC, we were able to modernized their system; save on water, improve productivity, reduce the overall footprint, and save on their energy usage. If you have a similar application, you can contact an Application Engineer at EXAIR. We will be happy to update your system.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb