As a widely used power source in the industrial field, compressed air accounts for 10%~35% of the total energy consumption in industrial production. 96% of the energy consumption of compressed air system is the power consumption of industrial compressor, and the annual power consumption of industrial compressor in China accounts for more than 6% of the total national power consumption. Air compressor operating costs by the procurement costs, maintenance costs and energy operating costs, by the theory of full life cycle evaluation, procurement costs account for only about 10%, while the energy cost is as high as 77%. It shows that China needs to vigorously improve the energy utilization efficiency of compressed air system while carrying out industrial and economic restructuring.

With the deepening of the understanding of compressed air and energy saving and emission reduction needs of enterprises, it is urgent to choose the appropriate technology to the existing system for energy-saving transformation has been to achieve the best energy-saving results. In the past two years, research on China’s industrial enterprises has shown that the demand for energy-saving renovation mainly comes from the following three aspects:

Air compressor energy consumption accounted for too high a proportion of enterprise power consumption; compressed air system supply instability, pressure fluctuations and other impacts on the normal work of the equipment; with the expansion of production scale, the enterprise of the original compressed air system to optimize the transformation to adapt to the growth of demand. Due to the characteristics of the enterprise compressed air system and the applicable energy-saving technology is different, in order to improve the success rate of the transformation, energy-saving transformation can not be blindly implemented. It is especially important to select suitable energy-saving measures based on comprehensive analysis, testing and evaluation of the whole system. The authors have analyzed and explored the characteristics and scope of application of some existing and emerging energy-saving technologies by investigating the use of compressed air in a large number of industrial enterprises.

System Energy Saving Strategy

Based on the theory of pneumatic system energy consumption evaluation and energy loss analysis, starting from the various aspects of the system composition, the overall energy-saving measures are taken as follows:

Generation of compressed air. Reasonable configuration and maintenance of different types of compressors, optimization of operation mode, daily management of air purification equipment. Transportation of compressed air. Optimization of pipeline network configuration, separation of high and low pressure supply pipelines; real-time supervision of air consumption distribution, daily inspection and minimization of leakage, improvement of pressure loss at joints. Use of compressed air. Improvement of cylinder driving circuit, use of energy-saving products developed for this industry, such as special air-saving valves for shelling cylinders in the electrolytic aluminum industry, as well as energy-saving air guns and nozzles. Compressor waste heat recovery. The heat generated during air compression is recovered by means of heat exchange, etc., and used for auxiliary heating and process heating, etc.

Generation of compressed air

1 Single air compressor energy saving

At present, the most widely used air compressors in industry are mainly divided into reciprocating, centrifugal and screw. Reciprocating type is still used in large quantities in some old enterprises; centrifugal type is widely used in textile enterprises with stable operation and high efficiency, but it is prone to surge when the system pressure changes suddenly. The main energy-saving measures used are: to ensure the cleanliness of the imported air, especially textile enterprises to do a good job of coarse filtration, in order to filter out a large number of short fibers in the air. Reduce the air compressor inlet temperature to improve efficiency. Lubricating oil oil pressure on the centrifuge rotor vibration has a big impact, the choice of lubricating oil containing antifoaming agents and oxidation stabilizers. Pay attention to the cooling water quality, reasonable cooling water discharge, planned water replenishment. The condensate discharge points of the air compressor, dryer, storage tank and pipe network should be discharged regularly. In order to prevent wheezing caused by rapid changes in air demand, etc., pay attention to adjusting the proportional band and integral time set by the unit, and try to avoid sudden reduction in air consumption. Select three-stage centrifuges with remarkable energy-saving effect, and try to use high-pressure motors to reduce line losses and keep the temperature rise of the air pressure station low.

Screw air compressor is widely used, the following focus on screw air compressor control mode comparison summary: analyze the current air compressor loading / unloading and constant pressure regulation problems, can be concluded: rely on mechanical means of regulating the inlet valve, air supply can not be quickly and continuously adjusted. When the amount of gas is constantly changing, the supply pressure inevitably fluctuates greatly. Pure frequency control is used to match the fluctuation of air consumption in the factory by adding a frequency converter to adjust the air production of the air compressor. The disadvantage is that the system is suitable for the situation that the fluctuation of the factory air consumption is not big (the fluctuation is 40%~70% of the single machine air production volume and the energy saving effect is the most significant).

2 Air compressor group expert control system

Air compressor group expert control system has become the new technology of air compressor group control and energy saving. The control system according to the pressure demand changes, Admiral control of different air compressors start and stop, loading and unloading, etc., to keep the system has always been the right number and capacity of the compressor in operation.

Home control system through the control of the frequency converter to change the speed of a single air compressor in the factory low-pressure gas supply system to control the air compressor unit time of gas production, matching the factory low-pressure gas supply system with small fluctuations in the amount of gas. Generally choose which air compressor frequency conversion transformation, need to be a professional system to carry out comprehensive testing and calculation to decide. Through the above analysis and comparison, can be found: many of our compressed air system energy efficiency has a lot of room for improvement. Compressor frequency conversion transformation can only achieve energy saving effect by combining with the operation of the enterprise’s own compressed air system, which needs to be fully tested and evaluated by professionals before use. Air compressor group expert control system is particularly suitable for multiple air compressors running at the same time, the implementation of step combination configuration, can well meet the needs of enterprises.

3 compressed air drying process improvement

At present, the most commonly used compressed air drying and processing equipment for enterprises is the refrigerated type, no heat regeneration type and micro-heat regeneration composite type, the main performance comparison is shown in the table below.

Energy-saving transformation of the line of defense to follow the following principles: If the original system of air is too high purity treatment, change to a lower matching treatment. Improve the drying process, reduce the pressure loss of the drying treatment link (pressure loss at the dryer of certain systems up to 0.05 ~ 0.1MPa), reduce energy consumption.

Transportation of compressed air

1 piping system piping system yajiang should not exceed 1.5% of the working pressure. Currently, many air pressure stations have no primary and secondary pipelines, too many unnecessary elbows and bends, frequent pressure pulsations, and serious pressure loss. Some of the pneumatic pipelines are buried in the trench and cannot be monitored for leakage. To ensure the system pressure demand in any case, the operation management personnel increase the operation pressure of the whole system by 0.1~0.2MPa, introducing artificial pressure loss. For every 0.1MPa increase in air compressor exhaust pressure, the power consumption of the air compressor will increase by 7%~10%. At the same time, the increase in system pressure increases air leakage. Energy-saving renovation measures: change the pipeline of branch arrangement into loop arrangement, implement separation of high and low pressure air supply, and install high and low pressure precision overflow unit; change the pipeline with large local resistance during energy-saving renovation, reduce the pipeline resistance, and purify the inner wall of the pipe by acid washing, rust removal, etc., so as to ensure that the wall of the pipe is smooth.

2 Leakage, leakage detection and plugging

Most of the factory leakage is serious, the leakage amount reaches 20%~35%, which mainly occurs in the valves, joints, triplets, solenoid valves, threaded connections and the front cover of the cylinder of each gas-using equipment; some of the equipment works under overpressure, unloads automatically, and exhausts frequently. The damage caused by leakage is almost beyond most people’s imagination. Such as automobile spot welding station of a welding slag in the gas pipe caused by a small hole of 1mm in diameter, the annual loss of electricity up to 355kWh, almost equivalent to two three-member family’s annual household electricity. Energy-saving measures: Install a flow measurement management system for the gas supply pipeline of the main generating workshop to determine the limit of process usage. Adjust the process gas consumption, minimize the number of valves and joints, and reduce leakage points. Strengthen management and use professional tools for regular inspections. In short, enterprises can use some professional testing equipment such as parallel access intelligent gas leakage detector, leakage point scanning gun, etc., to take measures to prevent the compressed air system from running, risking, dripping and leaking, accordingly carry out maintenance work and component replacement work.

Use of compressed air

Air guns are widely used in manufacturing finishing processes, machining and other process sites, and their air consumption reaches 50% of the total air supply in some industrial areas. In the process of using, there are such phenomena as too long air supply pipeline, too high supply pressure, using straight copper pipe as nozzle and unauthorized increase of working pressure by front-line workers, which cause huge waste of air.

Unreasonable phenomenon of using gas in pneumatic equipment is also more prominent, such as determining whether the workpiece is stuck in place of the gas back pressure detection, vacuum generator gas supply, etc. Zun uninterrupted gas supply phenomenon when not working. These problems exist especially in chemical tanks and other gas used for mixing, and in tire manufacturing, such as stereotypical inflation. Energy-saving reform measures: Use of new pneumatic nozzle energy-saving devices and pulse-type air guns. The use of specialized pneumatic equipment in specific industries, such as aluminum industry to promote the use of shelling cylinder special air-saving valve.

Air compressor waste heat recovery

According to the whole life cycle evaluation, 80%~90% of the electric energy consumed by air compressors is converted into heat and dissipated. The distribution of electric heat consumption of air compressor is shown in the figure below, excluding the heat radiated to the environment and stored in the compressed air itself, the remaining 94% of the energy can be utilized in the form of waste heat recovery.

Waste heat recovery is through the heat exchanger and other appropriate means of air compression process heat recovery used to heat air or water, typical use such as auxiliary heating, process heating and boiler make-up water preheating. With reasonable improvements, 50% to 90% of the heat energy can be recovered and utilized. Installation of heat recovery devices can effectively control the operating temperature of the air compressor at the optimal operating temperature, so that the lubricating oil working condition is better, and the exhaust volume of the air compressor will increase by 2%~6%. For air-cooled air compressor, you can stop the cooling fan of the air compressor itself and use the circulating water pump to recover the heat; water-cooled air compressor can be used to heat the cold water or space heating, and the recovery rate is 50%~60%. Waste heat recovery relative to electric heating equipment almost no energy consumption; relative to fuel gas equipment zero emissions, is a clean and environmentally friendly way of energy saving. Based on the theory of energy loss analysis of compressed air system, the existing unreasonable gas use phenomenon and energy saving measures of the enterprise are analyzed and summarized. In the enterprise energy-saving transformation, the first for different systems to do detailed testing and evaluation, on the basis of which the application of suitable optimization measures to achieve energy saving goals, can improve the operating efficiency of the entire compressed air system.