Technical Paper outline-P16452
●Abstract
Compressors have valves that are passive devices which work with a spring. The purpose of this project is to develop and build an active reciprocating compressor valve assembly that controls when to release air from a compressor. Our assembly consists of a designed test pressure vessel that enables the testing of the active pressure valve. The active valve uses a solenoid, powered with DC current to actuate four poppets as to when to release compressed air inside of the pressure vessel. LabVIEW software was utilized to generate a signal to the solenoids as to when to motion the poppets fore and aft in their cylindrical valve chambers.
This exhibit will display an actively controlled compressor valve assembly that was developed in Multidisciplinary Senior Design (MSD). It is very important that the actively controlled valve be able to achieve the same pressure profile as a passive compressor valve. This will be the first step towards proving that this technology can replace the traditional passive valves. This task is one of the main challenges for the team and the goal is to achieve this requirement through theory and simulation. Also, it is necessary to investigate different technologies that can be used to actuate the valve under the appropriate conditions (speed, temperature, pressure, etc.). After benchmarking and multiple concept selection processes, the team concluded that solenoids will provide the most efficient and appropriate actuation for our design. Due to safety issues, the designed active valve cannot be directly tested on the existing compressor. Therefore, a small vessel with inlet and suction valves will need to be designed to model the compressor and facilitate testing for compression cycle behavior.
●Background--Negar
Dresser-Rand is an American global supplier of custom engineered rotating equipment for many applications such as oil, gas, power and other industries worldwide. The company has been striving to provide the most efficient and reliable rotating products and lead in safety, quality, and cycle time[1].
In February 2011, a new Dresser-Rand single stage, dual acting reciprocating compressor was installed and commissioned on Rochester Institute of Technology’s (RIT) campus by a team of undergraduate engineers for their senior capstone design experience (Figure 1). This donation was a major part of an initiative to develop a strong collaboration between Dresser-Rand and RIT that began more than eight years ago. The intent of the compressor test cell at RIT is for both educational and research purposes.
Standard compressors operate with passive mechanical valves that utilize springs to direct airflow based on the pressure difference. Significant gains on efficiency and wear are possible if these valves are actively controlled (limiting impact velocities, chattering, etc.). The design, build, and test an active compressor valve assembly is necessary to investigate different technologies that can be used to actuate the valve under the appropriate conditions (speed, temperature, pressure, etc.
Figure 1: Passive pressure control valve
The goal of this project is to design and build an active reciprocating compressor valve assembly that controls when to release air from the compressor. The demonstration will require instrumentation to prove the design is meeting reciprocating compressor like specifications. Similar technology has been developed such as in 2007 by the Southwest Research Institute (SWI) by Dr. Klaus Brun ( where the individual valves were attached to a plate that was driven by an electromagnetic actuator. However, similar ideas have not yet been fully studied and are very costly.
●Design Process
○Customer Req. and Specifications/Eng. Req. (explain Func. decomp.)--Bob
The project was governed based upon the customer requirements that were implemented. These stipulations and request were utilized in the progress of the project so that the end product would suffice the customers needs. Below in Table 2, illustrates the needs of the customer.
Customer Rqmt. # / Importance / Description / Comments/StatusCR1 / 1 / Valves open and close simultaneously.
CR2 / 1* / Valve opening and closing are actively controlled / Very important!!!
CR3 / 3 / Pressure vessel simulates compressor cylinder
CR4 / 1 / Logs data in an easy to read format
CR5 / 2 / Demonstration system behaves similarly to the ESH-1 compressor.
CR6 / 3 / Active valve system conclusively performs better than passive spring
CR7 / 2 / Active valves assembly is interchangeable with passive valve assembly.
CR8 / 1 / Compatible with Labview
CR9 / 3 / Able to see components in use during a demonstration.
CR10 / 1 / Valves seat firmly against housing when closed
CR11 / 1 / Test bench is constructed to avoid user injury
CR12 / 2 / Valve opens and at a rate of 6Hz per second
Table 2: Active Reciprocating Compressor Valve Assembly Customer Requirements
The most critical customer requirement and goal of this project was to ensure that the valve will actuate open and closed all while being actively controlled. If this need was not meet the entire project would not be met and the creation of an active reciprocating valve would have failed. Other notable requirements are that the valve must open and close, otherwise the functionality of a the valve would cease to operate resulting in the failure of the assembly. In order to enable the universal installation and functionality of the valve, the end product must be able to demonstrate the same system behavior and result as the passive valve and the valve must be able to fit in all locations that the current passive valve exists. in order for the functionality to operate equal to or better than the current model, the active valve needed to seat firmly against the housing and possibly minimize the amount of ‘chatter’ that the passive valve displays. No injury must also be witnessed during the running of the valve or test bench.
In order for the engineers to be able to produce a valuable product for the customer, the engineers must generate guidelines and values that they must meet all while meeting the customer requirements. The values and requirements created can be seen in Table 3 below.
rqmt. # / Function / Engr. Requirement (metric) / Unit of Measure / Marginal Value / Ideal Value / Comments/StatusS1 / Measures Flow Rate / Vacuum Valve Flow Rate / ft3/h / 175.3 / 185.45 / Need modeling results
S2 / Safe / Reasonable Weight / lb / 75 / 50
S3 / Reasonable Size / ft3 / 3x3x4 / 2x2x3
S4 / Cylinder Pressure / psi / 7 / 5 / periodic wave
S5 / Cylinder Frequency / Hz / 2 / 6
S6 / Cylinder Size / in3 / 123.34 / 141.4
S7 / Number of discharge valves / -- / 1 / 4
S8 / Number of data points taken (sample frequency) / Hz / 12 / 100
S9 / Sensor / V / TBD / 0 to 10
S10 / Sensor resolution / % / TBD / <5
S11 / Vacuum Inlet Valve Flow Rate / ft3/h / 1844 / 1854
Table 3: Active Reciprocating Compressor Valve Assembly Engineering Requirements
From the table, the ideal values can be seen which are the expected numerical values to be delivered as well as the values that are satisfactory for the continuation and running of the project and is within the theoretical simulation. The ideal values, are the values that the original simulation and system were designed with. The marginal values were then determined while varying the ideal values until the simulation results were not desired.
Figure 2: Active Reciprocating Compressor Valve Assembly Functional Decomposition
○System Level Concept Selection--Bob
Through research of multiple forms of pressurized vessel system, a number of ideas were formulated to develop the system design. Concept differences involved a vacuum tank, vacuum valve, vessel pressure of 3psi and 18psi, inlet regulator, and a dynamic valve. Below in Figure 3, is the system pughchart the Active Reciprocating Compressor Valve Assembly.
Figure 3: Active Reciprocating Compressor Valve AssemblySystem Pugh Chart
From this figure, a comparison was made between all the different types of concepts generated in the brainstorming process. Critical criteria was selected and placed on the farthest left side of the table where the concepts were weighted against. Pluses, minuses, and zeros were used to rank how well the the concepts were when compared to Concept 3. When the ranking process was completed, the total minuses, pluses, and zeros, were tallied up to the respective column. With all the results gathered, the most positive concepts and ideas can be picked from the chart and concepts. Below in Figure 4, we can see Concept 2, which is the selected concept to create.
Figure 4: Active Reciprocating Compressor Valve AssemblySystem selected concept
Concept 2 illustrates the selected system with a regulator valve that introduces the pressurized air into the assembly, an actuator that releases the air to atmosphere and a vacuum valve that sets the pressure back to 0 psi in the tank. Within the tank is a pressure sensor to monitor the pressure within the vessel which intern returns a voltage reading to the external control system. The external control system then sends a signal out and controls the vacuum valve, regulator and actuator so that the vessel maintains a sinusoidal like curve.
○Simulation and Analysis---Negar
One of the important customer requirements is pressurizing the vessel in a way that it follows a compression cycle. Simscape simulation was done to understand the flow of air through the system and determine what combinations of valves and tanks can result in a compression cycle pattern.
The system is consisted of an inlet, suction, and outlet valve (which is the active valve designed by the team). The vessel size is 0.1ft^3. The pressure enters at 50 psig and pressurizes the vessel to 5 psig. Once the vessel reaches 5 psig, the outlet valve opens and reliefs the compressed air to atmosphere. After the outlet valve closes, the suction valve opens until the pressure inside the vessel is back to 0 psig. The graph below shows that the system has an overshoot value of about 1 psi, thus meaning that the pressure inside the vessel will reach 6 psig instead of 5. However the results are close to ideal and the overshoot can be neglected. The compression cycle repeats at a frequency of 4HZ, which is the customer's requirement.
The orifice area and mass flow rate values of inlet and suction valve that are obtained from this simulation model assisted the team in purchasing the suitable valves. Most importantly, the orifice area value of the outlet valve obtained from this simulation played a significant role in designing and dimensioning the active valve.
Figure 5: Model and Simulation of the Active Reciprocating Compressor Valve AssemblySystem
○Detailed Design
■Mechanical Design (components)--Ian
Valves
Figure 6: Solenoid Cover
The entire system is composed of two main portions: the valve assembly, which is what the projects is based upon, and the vessel, the container used to contain air for testing the valves.
Figure 7: Poppet
The Poppet is what is being actuated to open and close the valves. It has a gap in the center to hold neodymium, N52, magnets. The magnets are held in the poppet because of interference; the magnets are force-fit into the poppet. The material of the poppet, acetal, is a plastic, and when used in the brass solenoid covers, has a low coefficient of friction.
Figure 8: Solenoid Cover
The Solenoid Cover is a housing for the poppet, as well as a means to protect the solenoid from any elements coming from the compressor. The locating pin exists as a means to prevent the cover from rotating and twisting the wires connected to the solenoid.
Figure 9: Valve Assembly Bottom
The Valve Assembly Bottom is the housing unit for all of the solenoids and poppets. There are four locations to place solenoid covers, four holes to allow the compressed air to exit the assembly, and four more holes to align this piece, the valve assembly top, and the cover plate together.
Figure 10: Cover Plate
The Cover Plate is a meant to go between the two valve assembly halves. Its purpose is to secure the solenoid covers, preventing any translating motion. It is fastened down by a rim on the valve assembly top, as well as a screw/bolt in the center.
Figure 11: Valve Assembly Top
The Valve Assembly Top is the top half of the valve assembly. The four holes on the square area is for securing the valve assembly to the pressure vessel, while the ridge in the circular section is meant to house an o-ring, creating a seal to prevent the air from escaping within the vessel.
Figure 12: Vessel
The Vessel is where the air will be compressed. It is modeled so the volume is as close as possible to the volume of the compressor in possession by RIT.
■Electrical Design (components)--Keith + Chris
■Actuation: Solenoids+Displacement Measurement System-Bob
The Hall Effect sensor consist of a thin piece of semiconductor material such as gallium arsenide (GaAs), indium antimonide (InSb) or indium arsenide (InAs) passing a continuous current through itself. When the device is placed in a magnetic field, the flux lines exert a force on the semiconductor material which deflects the electrons to the ends of the semiconductor slab. As these electrons and holes move a voltage is produced between the two ends of the semiconductor material. The movement of electrons through the semiconductor material is affected by the presence of an external magnetic field. Below in Figure……….. We can see an image of a simple hall effect sensor.
Figure 13: Hall Effect sensor
The application of the hall effect sensor is endless and used in multiple applications. The auto industry has used this technology for shifting the vehicle into different gears, sensors that detect if doors are open or closed, and for determining vehicle handling monitoring the position of the steering column.. The cell phone industry has also used this technology in a similar manner in their flip phones. As the flip phones closed the screen is shut off when the hall effect sensor senses the magnetic field of the magnet in the ear piece and further shuts the screen off.
The application of the hall effect sensor for our project will be used to measure the magnetic field movement of the poppets inside the solenoid. The magnetic field will then induce a voltage that will then be measured and converted into a displacement.
The solenoid actuation will be driven with a magnetic force that is created through a solenoid, with the solenoid driven by a motor driver which is fed 36 volts from a power supply. The motor driver outputs a PWM which is controlled by a DAQ interfacing between a motor driver and a computer with LABVIEW. The actuation will be monitored with the use of a Hall Effect sensor which is atransducer that varies outputvoltage as it responds to a magnetic field.
■Power & Controls
Two power supplies were used in the integrated system in order for it to function properly and effectively. A high voltage 200W power supply unit which outputs 5.9A power supply was used to power the motor driver. The second power supply with a low voltage output was used to power the four Hall Effect Sensors.
■LABVIEW/DAQ
■PWM
■Relays
●Build and Integration process
●Problem Tracking-Bob
Problems were tracked and monitored through a matrix where a solution to the problem was the end result. Below in Figure….. is a sample page from the problem tracking matrix file utilized.
Figure 14: Problem Tracking
Such problems that occurred was the Solenoid cannot produce the expected amount of force, the solenoid cannot produce the expected amount of force that was calculated, Hall Effect sensor orders didn’t go through, the heat produced by the solenoid is affecting current draw and response time, among many other problems. The steps taken to determine a solution to the problems were consistent by analyzing the problem, generating potential solutions, selecting and planning a solution, implementing a solution and evaluating the solution. This method allowed the team to be consistent and through while analyzing problems and approaching efficient and working solutions.
Results and Discussions
●Conclusion & Recommendations
●Reference
○[1] Dresser-Rand
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●Acknowledgements
○Dr. Slack
○Dr. Day
○Dr. Whellin