Manufacturers Opportunity for savings is to recover waste heat from air compressors

Compressed air accounts for a fair amount of total energy costs for industrial manufacturers. 

Everything in our lives requires a regular check-up, and in most cases timely replacement. This safeguards proper functionality, and most importantly is responsible for the better performance. 

It is no different in the case of a production facility, automotive manufacturing plants, agriculture industry, refinery, food manufacturing plant, or any other place that requires their systems and equipment to work and perform its best. Uptime and production output are critical elements in every industry. 

Same applies to air compressors in a facility or production plant, as it is a vital component just like other utilities. The compressor system is no different from the circumstances mentioned above. The tools, controls, valves, production equipment, etc., that require compressed air from the system all depend on its condition and production output. If the machine runs without being monitored, it might not be able to fulfill the production demand. 

Also, Compressed air accounts for a fair amount of total energy costs for industrial manufacturers – typically about 12 percent and maybe as high as 40 percent in some facilities considering it is an area which could have a big impact on the compressors. 

If the compressor has been used for a long period of time and might not be giving desired output any longer, it means you need to get it replaced or find solutions to increase the output. 

Air demand in an industrial compressed air system typically oscillates. Using these patterns to reduce unloaded running hours is a first step to enhancing energy efficiency. Compressor controllers offer user-friendly ways to reduce unloaded running hours. If you have multiple compressors, then they should have been set up to do this automatically. But if there is no central controller, then the compressor pressure bands should have been set up in a cascade method, and the on-board controllers will stop the machines if they are not needed when the compressed air target pressure is achieved. 

If compressors are left running unloaded after working hours, they still use as much as 25 percent of the energy consumed at full load. What’s more, if there are leaks in the system, the compressors may switch to loaded running occasionally, consuming even more energy. 

The shorter the production time, the more you can save by switching off compressors instead of letting them run unloaded. If production is reduced but not stopped, a possibility would be to isolate areas of the factory that are not currently being used. 

The compressors may switch to loaded running occasionally, consuming even more energy. Alternatively, consider using a Variable Speed Drive compressor which matches your compressed air with your factory air demand. 

Eliminate air leaks 

Leakages are the biggest source of energy waste in older compressed air systems, with a leakage point as small as 3mm costing an estimated `4667/week in wasted energy. It is estimated that up to 20 percent of total compressed air consumption may be lost through leaks. 

If you are still working on site and have some spare time, we recommend taking the opportunity to detect the leaks in your system. For example, you could run your air compressor with no production to check for leaks. Fixing air leaks will start to save you money immediately. 

The pressure band 

As a rule of thumb for most compressors, a reduction of 1 bar in pressure (14.5 psi) will lead to a 7 percent saving in electricity consumption. The pressure settings of the compressor should be adjusted until the lowest pressure can be reached and the pressure band reduced without affecting the application. 

For centralised systems utilising multiple compressors, by using a central controller, the network can be set to run within a narrow pressure band which ensures that the compressed air network matches your precise needs. The controller can also allow you to manually or automatically create two different pressure bands to optimise energy use within different periods, drastically reducing energy costs at low-use times. 

Also, lowering the system pressure reduces the impact of leaks. A 1 bar pressure reduction decreases the impact of air leaks by 13 percent. 

Turn compression heat into useful energy with heat recovery 

One area that offers manufacturers a significant opportunity for savings is to recover the waste heat from air compressors. Without energy recovery, this heat is lost into the atmosphere via the cooling system and radiation. The amount of electrical energy that can be recovered depends on the size of the compressor and the running hours. Typical recoveries are between 70-94 percent. 

Recovering heat from compressed air reduces the need for purchasing energy, for example to heat hot water. It is this reduction that results in lower operating costs and CO2 emissions, also reducing your carbon footprint. 

• Approximately 70 percent of energy is recoverable from oil injected screw compressors, and up to 94 percent from oil-free water cooled screw compressors. 

Ensure correct type of compressor installed 

Most production processes require different levels of demand in different periods, which may mean that the compressor is running off-load or idle (not producing any compressed air) for long periods of time. Great savings can be made if a fixed speed compressor can be replaced by a variable speed drive unit as it only produces compressed air as and when required. This also minimises offload running of the compressor, which is known to waste energy. 

• A VSD compressor saves an average 35 percent energy and a VSD+ unit can save as much as 50 percent compared to a fixed speed unit, even at full load. 

As a fixed speed compressor has a fixed amount of motor starts an hour, the compressor runs offload for a set time which limits the number of motor starts to ensure overheating of the motor does not occur. As a VSD unit ramps up and down in a controlled fashion, the maximum number of starts and stops per hour may be increased, and it also avoids peaks in current when starting. 

Impact of regular maintenance 

The best way of taking care of your compressed air availability is by taking the best care of your compressed air equipment. This means investing in regular preventative maintenance, which will sustain the efficiency that you have gained by purchasing a new compressor or improve the performance of an older unit. 

Whether you prefer to purchase spare parts only and perform maintenance in house, sign up to a planned maintenance program at predetermined intervals from the manufacturer or approved distributor, or choose a total responsibility package that covers breakdowns and leaves no room for surprises, the main thing to remember is that reduced compressor performance is not inevitable as the machine gets older. Regular servicing will improve your equipment uptime and energy efficiency: the opposite could lead to more downtime, increased energy consumption and potentially a breakdown.