Industrial Compressed Air Systems Research Articles

Exhaust Air Recovery System from the Utilisation Stage of Pneumatic System in Double Transmission Double Expansion Approach

Pneumatic machines and systems are highly popular in the automation and mechanisation of production lines in many industry sectors, such as, e.g., food, automotive, production, and packaging. However, the energy efficiency of the pneumatic system is very low at about 10 to 20% The exhaust air from pneumatic machines has high energy, which is considered waste. This study introduces a novel energy recovery machine designed for integration into industrial compressed air systems. The authors describe the potential of the recovery machine within an industrial environment and present a developed exhaust air recovery system which collects exhaust air and converts it into electricity. Comprehensive industrial tests were conducted to evaluate its performance. The results, along with a detailed analysis, are presented, thereby showing there machine’s capabilities in recovering energy from compressed air processes. This research provides valuable insights into the practical implementation and benefits of deploying such energy recovery systems at an industrial scale. The findings demonstrate the machine’s potential to enhance energy efficiency and reduce operational costs in a wide array of industrial applications that are reliant on compressed air.

Load sharing energy savings methodology for systems with multiple centrifugal compressors

Most industrial compressed air systems (CASs) use multicompressor systems to supply air in a common header to be distributed to end users. Screw compressors are reliable and relatively less maintenance-intensive and thus are widely popular. However, CASs with high flow requirements invariably employ centrifugal compressors because of economic power consumption characteristics near the designed flow range. Nonetheless, air requirements vary during production, which forces centrifugal compressors to operate far from the best efficiency point. The resulting nonoptimized CAS wastes energy. This research investigates a meta-control strategy for a CAS that employs multiple centrifugal compressors.Published literature shows a significant gap in identifying the importance and implementation of load sharing in centrifugal CASs to achieve energy savings. This research develops a generic methodology and model to identify an operating combination of compressors to optimize the power requirement. The model is used to examine the system characteristics of all centrifugal CASs. Finally, the model is applied to an operating scenario found in a large automotive assembly facility during CAS assessment. The model is used to identify possible energy and power savings. This study found that the implementation of a load sharing strategy could save 8.5% in energy and 7.4% in peak demand. This result will also correspondingly reduce the carbon footprint of the CAS.

Exergy analysis of pressure reduction, back pressure and intermittent air supply configuration of utilization/expansion stage in compressed air systems

Despite their many advantages, industrial compressed air systems are characterized by high energy consumption and very low energy efficiency. This is primarily due to the oversizing of pneumatic actuators, leading to excessive compressed air consumption in the utilization stage. Various methods have been proposed in the literature to address this issue, which can be classified into three groups: supply pressure reduction, back pressure increase, and intermittent power supply. However, no exergy analysis compares these methods in the utilization stage of a pneumatic system was performed. In this study, we conducted an exergy analysis to compare the exergy consumption and exergy savings of different pneumatic system configurations: the classic configuration, supply pressure reduction, back pressure increase, and intermittent power supply. The paper shows the most key places in CAS in terms of exergy losses, which result mainly from dead volumes, outlet loss and oversizing of components such as directional control valve, distributed pneumatic line and actuator. Losses in those components can amount to over 80% of input exergy and can be reduced even 3–9 times. Exergy evaluation of oversizing configurations showed that the highest exergy savings were obtained for a back pressure configuration (77%) and intermittent air supply (75%). The exergy savings for the pressure reduction configurations amounted to almost 50%. The paper presents mathematical models for several individual pneumatic components, including the actuator, directional control valve, muffler, pneumatic line and pressure reducer. The demonstrated mathematical model and exergy analysis can play a instrumental role in evaluating the exergy efficiency and optimization of a pneumatic system.

Isobaric storage of compressed air: Introduction of a novel concept based on phase change materials and pressure equalizing modules

In industrial compressed air systems (CAS), compressed air receivers have a significant impact on the overall energy efficiency. Isobaric compressed air receivers have the potential to increase the amount of stored air significantly and, hence, the energy efficiency can be improved compared to the usage of conventional isochoric compressed air receivers. In this work, we propose a novel concept of an isobaric compressed air receiver based on pressure equalizing modules (PEQM). These PEQM are filled with a condensable gas – in this work called phase change material (PCMl/g) – and are placed inside the receiver. During the charging and discharging of a compressed air receiver equipped with PEQM, the PCMl/g condenses or evaporates, respectively. Due to the large volume change during the phase change of the PCMl/g air can be stored isobarically. However, a proper selection of suitable PCMl/g is crucial for efficient and safe use. Therefore, we introduce a three-step selection process based on an adapted digital-logic method. In this selection process, qualitative (e.g. flammability) and quantitative (e.g., heat of condensation) properties are considered. As a result, R-1234ze(E) is selected as PCMl/g which owns a vapor pressure of 800 kPa at a temperature of 314.7 K. First experiments with the novel PEQM filled with R-1234ze(E) have been conducted in a lab-scale test plant and the results are shown in this work. The storage capacity of the test plant has been increased by 37.9 %. Additionally, the phase change of the PCMl/g during charging and discharging has been observed. However, the phase change is not isobaric yet. Temperature changes during the phase change inside the PEQM hinder the isobaric storing of the working gas. Therefore, proper heat management inside the PEQM is necessary, for example, by using a second phase change material for heat storage.

A research on the easy-to-use energy efficiency performance indicators for energy audit and energy monitoring of industrial compressed air systems

Compressed air systems have a high energy transfer capacity. They are widely used in the manufacturing industry due to being clean, dependable, and simple-to-use. On the other hand, these systems are among the most significant energy consumers in the manufacturing sector because they are inefficient with high electricity usage and high CO2 emissions. As a result, all kinds of the energy efficiency enhancements in these systems promote cleaner production by lowering total energy consumption and CO2 emissions in factories. In this paper, the energy-saving potential and carbon emissions of Compressed Air Systems are investigated using data from in-situ energy audits. A simple set of equations is proposed to calculate the mass flow rate of air leakage. The sound intensity (dB) obtained from ultrasonic flow measurements were used as the input of the equation set. Furthermore, two new Energy Performance Indicators have been proposed to guide energy audit evaluation and continuous monitoring of the energy efficiency of Compressed Air Systems in industrial facilities. The new evaluation criteria “Specific Compressed Air Savings” and “Specific Leakage Savings” provide a comparison tool to help decision-makers with their compressed air system investment decisions. Using the “Specific Compressed Air Savings” and “Specific Leak Savings” parameters, the analysis method is demonstrated for an example industrial plant. The facility's specific compressed air and leakage savings are calculated as 0.0067 TOE/ton and 0.0035 TOE/ton, respectively.

Regression analysis of the operational parameters and energy-saving potential of industrial compressed air systems

The electricity consumption of compressed air (CA) production and utilisation systems is high, due to an absence of suitable recovery methods and proper measurements in most industrial plants. This situation results in high costs of production and reduced profits. In our study, we therefore investigate the energy-saving potential of a CA system with the aim of reducing electricity consumption in an industrial facility. Our study consists of two parts: in the first stage, we evaluate the applicability of methods such as elimination of leakage in distribution lines, loaded-unloaded operation of compressors, and the use of waste heat recovery system methods, both physically and economically, while in the second, we examine the correlations between leakage airflow rate, noise, and system pressure in a general CA system and carry out regression analyses, using the SPSS (Statistical Package for Social Sciences) software program, for the first time. Our results suggest that optimised and improved CA systems are energy-saving solutions when applied in industrial plants. We demonstrate that there are strong correlations between the system pressure, air leakage diameter, noise, and annual leakage cost in industrial CA systems. The relationships between these variables can be expressed as a power model (Y=β×Xn).

Reducing Risk and Increasing Reliability and Safety of Compressed Air Systems by Detecting Patterns in Pressure Signals

This paper investigates the design of a classifier that effectively identifies undesired events by detecting patterns in the pressure signal of a compressed air system using a continuous wavelet transform. The pressure signal of a compressed air system carries useful information about operational events. These events form patterns that can be used as ‘signatures’ for event detection. Such patterns are not always apparent in the time domain and hence the signal was transformed to the time-frequency domain. Data was collected using an industrial compressed air system with load/unload control. Three different operating modes were considered: idle, tool activation , and faulty. The wavelet transforms of the pressure signal revealed unique features to identify events within each mode. A neural network classifier was created to detect faulty compressed air system behaviourbehaviour. Future work will investigate the detection of more faults and using other classification algorithms.

Real Time Energy Performance Control for Industrial Compressed Air Systems: Methodology and Applications

Most manufacturing and process industries require compressed air to such an extent that in Europe, for instance, about 10% of the total electrical energy consumption of industries is due to compressed air systems (CAS). However, energy efficiency in compressed air production and handling is often ignored or underestimated, mainly because of the lack of awareness about its energy consumption, caused by the absence of proper measurements on CAS in most industrial plants. Therefore, any effective energy saving intervention on generation, distribution and transformation of compressed air requires proper energy information management. In this paper we demonstrate the importance of monitoring and controlling energy performance in compressed air generation and use, to enable energy saving practices, to enhance the outcomes of energy management projects, and to obtain additional benefits for non-energy-related activities, such as operations, maintenance management and energy accounting. In particular, we propose a novel methodology based on measured data, and baseline definition through statistical modelling and control charts. The proposed methodology is tested on a real compressed air system of a pharmaceutical manufacturing plant in order to verify its effectiveness and applicability.

Time-Discrete Modelling of Industrial Compressed Air Systems Based on Equivalent Circuits

Compressed air systems (CAS) on industrial plants consist of air compressors, compressed air reservoirs, compressed air lines and auxillaries as dehumidifiers, dust collectors, pneumatic oilers and pressure controllers. It is assumed that given suitable dimensioning, those industrial compressed-air systems can be used for demand side management purpose. In industrial CAS energy is transmitted by means of pressure difference and volumetric flow rate of the transmission medium compressed air. Alike electric circuits, they consist of various functional components which are flowed through by the compressed air. Furthermore the application of Kirchhoffs laws is possible to those systems. Hence, approximation of the behavior of industrial CAS is possible by arranging and connecting those components in an equivalent circuit diagram. As additional state variables of compressed air as humidity, temperature as well as contents of water, oil and dust are also to be considered, modeling of the individual components is more extensive. A general, abstract approach for the description of the individual components in the form of blackbox representations is outlined.

Demand-side-management by Flexible Generation of Compressed Air

Industrial compressed air systems embrace significant potential for saving both energy and cost due to their share of approximately 7% of the total industrial electricity consumption in Germany. As in electric energy systems based on renewable generation plants supply and demand often do not occur in the same period of time, volatile prices occur and demand side management is gaining importance. Decentralized automation offers opportunities in industrial environments for control of the equipment according to availability of electrical energy. Product-service systems on industrial plants supply manufacturing equipment with compressed air, nitrogen and other technical gases, which partly can be obtained from air by deposition processes. Those systems consist of air compressors, gas separators, reservoirs and lines. With suitable dimensioning and by equipping with automation technology those product-service systems can be used for demand side management purpose. In addition to basic operating parameters like current air pressure and status, those systems can process further information and create, for example, profiles on compressed air consumption over time. By enriching those profiles with data on pressure, volumes, system restrictions and current production requirements, the system control can identify the available potential for demand side management. Evaluation of operational strategies has to optimize conflicting objectives within the triangular relationship of storage design, control of the production according to price prospects and influencing or predicting the use of compressed air.

A cost-effective compressed air generation for manufacturing using modified microturbines

Compressed air is an irreplaceable energy source for some manufacturing processes, and is also common in applications even when there are alternatives. As a result, compressed air is a key utility in manufacturing industry, but unfortunately the cost of compressed air production is one of the most expensive processes in a manufacturing facility. In order to reduce the compressed air generation cost an unconventional way using a microturbine configuration is proposed. The concept is based on an extraction of a certain amount of compressed air from/after the compressor with the residual air flowing to the turbine to produce sufficient back power to drive the compressor. A thermodynamic and life cycle analysis are presented for several system variations, including a simple cycle without a recuperator and a complex configuration with an intercooler, recuperator and reheating. The study is based on the typical requirements (i.e. quantity, pressure) for a small to medium sized industrial compressed air system. The analysis is focused on the North American market due to the low price of natural gas. The lowest life cycle cost alternative is represented by a microturbine concept with a recuperator, air extraction after partial compression, intercooler and aftercooler. A comparison of an electric motor and conventional microturbine prime movers demonstrates the economic benefit of the proposed compressed air generation method, for the design parameters and utility prices considered.

Smart Factory Meets Smart Grid: Cyber-Physical Compressed Air Systems Enable Demand Side Management in Industrial Environments

In electric energy systems based on renewable generation plants supply and demand often do not occur in the same period of time. Consequently demand side management is gaining importance whereby decentralized automation offers opportunities in industrial environments. Compressed air systems on industrial plants consist of air compressors, compressed air reservoirs and compressed air lines. With suitable dimensioning those industrial compressed-air systems can be used for demand side management purpose. As power consumption of industrial air compressors ranges between a few and several hundred kilowatts each, swarms of communicatively connected air compressors can contribute to the stabilization of power grids. To avoid costly production downtime it is to ensure, that a reliable, non-disruptive supply of compressed air can be maintained at all time. Industrial compressed air systems equipped with automation technology and artificial intelligence, which hereinafter are referred to as Cyber-Physical Compressed Air Systems (CPCAS), allow new business models for utilities, industrial enterprises, compressor manufacturers and service providers. In addition to basic operating parameters like current air pressure and status, those systems can process further information and create, for example, profiles on compressed air consumption over time. By enriching those profiles with data on pressure, volumes, system restrictions and current production requirements (plans), the CPCAS can identify the available potential for demand side management. Ipso facto predictive power on electricity consumption is increasing. By providing the information obtained to the power company or a service provider, savings in electricity costs may be achieved. Expenses within the industrial company may be lowered further as compliance with agreed load limits is being improved by automatic shutdown of air compressors upon reaching the load limit. Within this article the structure of the aforementioned Cyber-Physical Compressed Air Systems is presented in more detail, relations between the major actors are being shown and possible business models are being introduced.

Experimental and numerical analyses on a plate heat exchanger with phase change for waste heat recovery at off-design conditions

This paper analyzes the performances of an evaporator for small scale waste heat recovery applications based on bottoming Organic Rankine Cycles with net output power in the range 2-5 kW. The heat recovery steam generator is a plate heat exchanger with oil as hot stream and an organic fluid on the cold side. An experimental characterization of the heat exchanger was carried out at different operating points measuring temperatures, pressures and flow rates on both sides. The measurement data further allowed to validate a numerical model of the evaporator whereas heat transfer coefficients were evaluated comparing several literature correlations, especially for the phase-change of the organic fluid. With reference to a waste heat recovery application in industrial compressed air systems, multiple off-design conditions were simulated considering the effects of oil mass flow rate and temperature on the superheating of the organic fluid, a key parameter to ensure a proper operation of the expansion machine, thus of the energy recovery process.

Environmental Impact of an Industrial Compressed Air System with a Solar Powered Compressor in South Africa

Almost 14% of the electricity generated by the national energy supplier (Eskom) in South Africa is sold directly to the mining sector and almost 20% is utilized directly by the compressed air systems of the mining sector. The industrial compressed air systems in South Africa therefore have a substantial impact on the environment in terms of emissions output. In this paper a solar powered compressor is installed parallel to an existing industrial compressed air system. The environmental (emissions) impact and energy consumption of the industrial compressed air system with the solar powered compressor is calculated and the results are provided. It is shown from the results that the solar powered air compressor improved the overall system efficiency and lowered the carbon footprint of the industrial compressed air system. The impact of the energy improvement on the amount of trees required to offset the calculated amount of CO2 is also provided.

Microphone Arrays as a Leakage Detection Tool in Industrial Compressed Air Systems

Compressed air energy is expensive, but common in industrial manufacturing plant. However, a significant part of the generated compressed air energy is lost due to leakage. Best practice requires ongoing leak detection and repair. Leak detection in the ultrasonic frequency range using handheld devices is possible only over short distances as associated high-frequency sound is rapidly attenuated by atmospheric absorption. Pressurized air escaping to ambience also generates frequencies below 20 kHz. In this paper beamforming—a well known method for generating noise maps—is tested as a tool for localization of compressed air leaks at larger distances in the audible frequency range. Advanced beamforming methods in both time domain (broadband) and frequency domain (narrowband) have been implemented in a variety of situations on a laboratory experimental rig with several open blows representing leakage in a noisy environment similar to a factory setting. Based on the results achieved it is concluded that the microphone array approach has the potential to be a robust leak identification tool. The experience gained here can also provide useful guidance to the practitioner.

A practical approach to investigating energy consumption of industrial compressed air systems

While there are several best practice standards available for minimizing the energy requirement for compressed air use in an industrial context, moving to best practice often requires investment and operational change. In production facilities, there is often a reluctance to commit to this type of change without a clear view of the benefit. Furthermore, there is very little detailed information available in the open literature that allows even a qualitative assessment of priorities. In order to address this shortcoming, a practical approach is proposed to provide detailed compressed air consumption information throughout an industrial site. The energy of the compressed air is evaluated at each key element of the system and the typical end-use application profile assessed. Simple models of the consumption rates are used to relate duty cycle and device count with actual total consumption. This approach is complemented with a novel method of assessing the leak rate from the entire system, based on the pressure decay time. The method, referred to as the ‘end use catalogue’ has been demonstrated at a manufacturing site with a wide range of compressed air applications. The model has been used to identify the most significant energy-intensive compressed air applications and possible strategies to reduce the energy requirement. In the particular site used as a demonstration, it was found that open blowing operations (e.g. fluidizing) are the largest consumers of compressed air which are amenable to intervention. System leakage accounts for almost 21 per cent of the compressed air generated, representing an energy input of 432 kWh per day. It is concluded that this approach can help to identify priorities for optimizing compressed air use at an industrial site without compromising the production yield.