2.Energy-saving techniques to improve the energy efficiency of air dryers
As a key equipment for compressed air purification in industrial production, the energy consumption of cold dryers accounts for a large proportion of the entire compressed air system. Effectively improving the energy efficiency of air dryers can not only significantly reduce the operating costs of enterprises, but also conform to the current development trend of green and low-carbon. The following will explain the various energy-saving techniques to improve the energy efficiency of air dryers in points:
2.1 Accurate selection and optimized configuration: the cornerstone of energy saving
The correct selection of equipment is the first and most important step to achieve energy saving. When many companies purchase air dryers, they often have the mentality of “preferring large to small”, which leads to the equipment processing capacity far exceeding the actual demand, resulting in serious energy waste, the so-called “big horse pulling a small cart”. On the contrary, if the selection is too small, it may lead to unstable dew point and affect the production process.
Calculate the processing volume according to actual needs: Accurately evaluate the actual gas consumption and maximum instantaneous flow rate of compressed air on the production line. This requires detailed statistics and analysis of the types, quantities, working cycles, etc. of gas-using equipment. At the same time, future expansion needs should be considered, but blindly reserving too much margin should be avoided. The calculation formula usually involves the conversion of standard flow (Nm³/min) and the correction of parameters such as inlet temperature, pressure, and ambient temperature. Only when the processing volume is accurately matched with the actual demand can the equipment be prevented from running under low load, thereby reducing unnecessary energy consumption.
Choose high-efficiency and energy-saving air dryers: There are many types of air dryers on the market with different energy-saving characteristics.
Variable frequency air dryers: The core lies in its variable frequency compressor technology. When the compressed air processing volume is lower than the rated value, the variable frequency compressor can automatically adjust the operating frequency to match the actual load demand, thereby reducing the cooling capacity output and significantly reducing energy consumption. This model is particularly suitable for occasions with large fluctuations in gas consumption, and the energy saving effect can reach 20%-50%.
Heatless regeneration adsorption air dryer (combined with cold dryer): Although the title is air dryer, this is mentioned to emphasize the energy saving of the system. In some occasions where a lower dew point is required (such as below -40℃), the cold dryer, as a pretreatment device, can greatly reduce the load of the subsequent adsorption dryer, thereby indirectly reducing the regeneration energy consumption of the adsorption dryer.
Modular air dryer: For occasions where the gas consumption varies greatly, multiple small air dryers are connected in parallel, and the corresponding modules can be started and stopped according to the actual gas consumption to avoid large machines with small usage.
Optimize the matching of air dryers and air compressors: The air dryer should work in conjunction with the air compressor. Ideally, the processing capacity of the cold dryer should be slightly greater than or equal to the exhaust volume of the air compressor. If the processing capacity of the air dryer is much smaller than that of the air compressor, it will cause incomplete compressed air processing and affect the dew point; if the processing capacity of the cold dryer is too large, it will cause energy waste. At the same time, the impact of the exhaust temperature of the air compressor on the cold dryer should be considered. The high-temperature gas entering the air dryer will increase its load.
Application of precooler: In some extremely high temperature and high humidity environments, or when the exhaust temperature of the air compressor is too high, setting an independent precooler before the inlet of the cold dryer can effectively reduce the temperature of the air entering the cold dryer, thereby greatly reducing the refrigeration load of the cold dryer and improving its efficiency. The precooler can use cooling water or ambient air for precooling.
Avoid over-drying (dew point setting): The main function of the cold dryer is to reduce the dew point of compressed air to prevent condensation from forming in the pipeline and equipment. However, many users tend to set the dew point too low, far below the actual process requirements. For every 1°C decrease in dew point, the energy consumption of the cold dryer will increase significantly. Therefore, it is a simple and effective way to save energy to accurately understand the minimum requirements for dew point at each gas point and appropriately increase the set dew point of the cold dryer on this basis. For example, for most general pneumatic tools and valves, a pressure dew point of +3°C is sufficient; while for some precision instruments or spraying processes, a dew point of -20°C or lower may be required. Reasonable setting of the dew point according to actual needs is the key to avoiding “excessive consumption”.
2.2 Refined management of operating parameters: dynamic energy saving
During the operation of the cold dryer, its energy consumption is affected by a variety of operating parameters. Dynamic energy saving can be achieved by finely managing these parameters.
Maintain stable inlet temperature and pressure: Fluctuations in inlet temperature and pressure will directly affect the refrigeration load of the cold dryer. The higher the temperature and the lower the pressure, the greater the load of the cold dryer and the higher the energy consumption. Therefore, it is necessary to ensure that the gas temperature and pressure output by the air compressor are relatively stable to avoid drastic fluctuations. For high temperature and high humidity conditions, consider adding a pre-cooling device.
Adjust operating parameters according to changes in ambient temperature: The refrigeration effect of the cold dryer is significantly affected by the ambient temperature. At high temperatures in summer, the heat dissipation efficiency of the condenser decreases and the load of the refrigeration system increases; at low temperatures in winter, the condensation effect may be too good and even cause ice. Some intelligent cold dryers can automatically adjust the cooling capacity or fan speed according to the ambient temperature to maintain the best operating state. For equipment that does not have this function, the manual adjustment parameters should be optimized in different seasons.
Avoid frequent start and stop: The cold dryer will generate a large impact current at the moment of starting, and frequent start and stop will accelerate the wear of components. The equipment should be kept running continuously and stably as much as possible. For occasions with intermittent gas consumption or large fluctuations in gas consumption, you can consider using a variable frequency cold dryer or adopting a joint control mode of multiple small units.
Implement variable frequency control or segmented control:
Variable frequency control: For non-variable frequency cold dryers, if the gas consumption fluctuates greatly, you can consider frequency conversion of its refrigeration compressor. The frequency converter adjusts the compressor speed according to the actual load to achieve stepless regulation of the cooling capacity, thereby significantly reducing the energy consumption under partial load.
Segmented control: For cold dryers with large processing capacity, if there are multiple refrigeration circuits inside, energy consumption can be optimized through segmented control. When the gas consumption decreases, some refrigeration circuits can be closed to allow the remaining circuits to operate in the high-efficiency zone to avoid inefficient operation of the overall equipment.
2.3 Daily maintenance and care: extend life and maintain high efficiency
Good daily maintenance is the key to ensure the long-term and efficient operation of the cold dryer, and it is also an important means to prevent the invisible increase in energy consumption.
Clean the condenser regularly: The condenser is the core component of the dryer’s heat dissipation. Dust, oil or blockage on its surface will lead to poor heat dissipation, reduced refrigeration efficiency, increased load on the refrigeration compressor, and increased energy consumption. Compressed air, soft brush or special cleaning agent should be used to clean the condenser fins regularly to ensure good heat dissipation. For water-cooled dryers, the cooling tower and water circuits need to be cleaned regularly to prevent scale formation.
Regularly check and replace the filter element: Pre-filters and precision filters are usually configured in front of the dryer to remove solid particles, oil mist and water droplets in the compressed air. Blockage of the filter element will increase the pressure drop and increase the workload of the air compressor, thereby indirectly increasing the energy consumption of the entire system. The filter element should be checked and replaced regularly according to the running time or pressure difference indicator to ensure smooth air circulation.
Check the amount of refrigerant and whether there is any leakage: Refrigerant (refrigerant) is the core medium of the dryer’s refrigeration cycle. Insufficient refrigerant will lead to reduced refrigeration efficiency, the dryer cannot reach the set dew point, and the compressor will run longer and energy consumption will increase. The refrigerant pressure should be checked regularly, and the refrigerant should be repaired and replenished in time when a leak is found. This requires professionals to use special tools to operate.
Check the drain valve regularly to ensure smooth drainage: The condensate generated by the dryer needs to be discharged in time. If the drain valve is blocked or faulty, the condensate will accumulate in the heat exchanger, affecting the heat exchange efficiency and even causing the “secondary water” problem. The operation of the drain valve should be tested manually or automatically regularly to ensure its normal operation.
Establish a complete equipment maintenance file: Record the equipment’s operating time, maintenance date, replacement parts, fault phenomena and treatment methods, etc. This helps to track the equipment’s operating status, predict maintenance cycles, and provide data support for future fault diagnosis and energy-saving transformation.
2.4 Auxiliary equipment and system optimization: energy saving from a global perspective
The dryer is not an isolated device, and its energy efficiency is also affected by the configuration of the entire compressed air system. Optimization at the system level often brings unexpected energy-saving effects.
Optimize the layout of compressed air pipelines to reduce pressure loss: Too long pipelines, too many elbows, too small pipe diameters, and pipeline blockages can all cause significant pressure losses. Every increase of 0.1MPa in pressure loss means that the air compressor consumes about 7% more electricity. Therefore, the pipeline design should be optimized, the appropriate pipe diameter should be used, the elbows should be reduced, and the inside of the pipeline should be cleaned regularly to ensure that the compressed air reaches the gas point with minimal resistance.
Timely handling of compressed air system leaks: Leakage in the compressed air system is a common “invisible waste”. A small hole may waste thousands or even tens of thousands of yuan in electricity bills every year. Using an ultrasonic leak detector to regularly detect leaks in the entire compressed air system and repair them in time is an immediate energy-saving measure.
Reasonable configuration of gas storage tanks: The function of the gas storage tank is to stabilize the air pressure, buffer the fluctuation of gas consumption, and store a part of the compressed air. Reasonable configuration of the volume of the gas storage tank can reduce the frequent loading and unloading of the air compressor, so that it can operate in a more stable state, thereby reducing energy consumption. At the same time, the gas storage tank can also further cool the compressed air, which is beneficial to the operation of the cold dryer.
Utilize waste heat recovery technology: Although it is mainly for air compressors, for large industrial systems, cold dryers will also generate a certain amount of heat during operation. If conditions permit, consider recycling the heat discharged by the cold dryer, such as for preheating boiler water, winter heating or providing domestic hot water, so as to achieve cascade utilization of energy and further improve the energy efficiency of the overall system.
Introducing Internet of Things and big data technology for remote monitoring and management: In the context of modern Industry 4.0, by installing sensors and intelligent modules on the cold dryer, real-time remote monitoring of the equipment operating status (such as dew point, temperature, pressure, current, etc.) can be achieved. Big data analysis can help enterprises discover energy consumption anomalies, predict equipment failures, and optimize operation strategies, thereby achieving refined management and continuous energy saving.
