Proceedings of the Multi-Disciplinary Senior Design Conference Page 13

Proceedings of the Multi-Disciplinary Senior Design Conference Page 13

Project Number: P16452

Proceedings of the Multi-Disciplinary Senior Design Conference Page 13

Active Reciprocating Compressor Valve Assembly

Mechanical Engineering
Ian Nanney
Negar Salehi
Robert Osborn / IMAGE
Electrical Engineering Keith Leung
Christopher Reynolds

Proceedings of the Multi-Disciplinary Senior Design Conference Page 13

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 (http://www.swri.org/9what/releases/2007/plateval.htm) 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. Requirements

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/Status
CR1 / 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/Status
S1 / 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

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 pugh chart the Active Reciprocating Compressor Valve Assembly.

Figure 3: Active Reciprocating Compressor Valve Assembly System 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 Assembly System 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

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 Assembly System

Detailed Design

Figure 6: Solenoid Cover

The entire system is composed of two main portions: the valve assembly, which is what the project 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. The chamfer at the top of the poppet is there to allow the poppet to center itself to the hole. The chamfer also allows for the poppet to wedge itself into the hole easier, allowing for easier deformation of the plastic for sealing to occur.

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. The flange locates the solenoid cover within the bottom piece of the valve assembly to allow the poppets to have the same base location to measure displacement. The part is made from brass because of the low coefficient of friction with plastic and due to it being non-magnetic, so it won’t interfere with the solenoid. Around the outside of the cover is a solenoid, which is being used to actuate a poppet on the inside of the cover.

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 via bolts. Within the largest holes, there is a ledge to locate the solenoid covers vertically, to small through holes to allow for wires for the solenoids, and one more hole to locate the solenoid covers. In the center of the part is a hole for a threaded insert, due to being unable to create threads in the plastic piece. The piece is made from HDPE for two reasons: it reduces the weight of the overall system, and it allows for better sealing with the top portion of the part by having a softer material mating with a harder material. The material on the outside diameter is removed in order to reduce the weight. The ledge in the center of the part, with a diameter of 6”, is to give the poppets room to move and to give air pathways to exit the system.